Allow AI interactions to be proxied through Zed's server so you don't need an API key (#7367)

Co-authored-by: Antonio <antonio@zed.dev>

Resurrected this from some assistant work I did in Spring of 2023.
- [x] Resurrect streaming responses
- [x] Use streaming responses to enable AI via Zed's servers by default
(but preserve API key option for now)
- [x] Simplify protobuf
- [x] Proxy to OpenAI on zed.dev
- [x] Proxy to Gemini on zed.dev
- [x] Improve UX for switching between openAI and google models
- We current disallow cycling when setting a custom model, but we need a
better solution to keep OpenAI models available while testing the google
ones
- [x] Show remaining tokens correctly for Google models
- [x] Remove semantic index
- [x] Delete `ai` crate
- [x] Cloud front so we can ban abuse
- [x] Rate-limiting
- [x] Fix panic when using inline assistant
- [x] Double check the upgraded `AssistantSettings` are
backwards-compatible
- [x] Add hosted LLM interaction behind a `language-models` feature
flag.

Release Notes:

- We are temporarily removing the semantic index in order to redesign it
from scratch.

---------

Co-authored-by: Antonio <antonio@zed.dev>
Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Thorsten <thorsten@zed.dev>
Co-authored-by: Max <max@zed.dev>

crates/assistant/src/saved_conversation.rs

@@ -0,0 +1,121 @@
+use crate::{assistant_settings::OpenAiModel, MessageId, MessageMetadata};
+use anyhow::{anyhow, Result};
+use collections::HashMap;
+use fs::Fs;
+use futures::StreamExt;
+use regex::Regex;
+use serde::{Deserialize, Serialize};
+use std::{
+    cmp::Reverse,
+    ffi::OsStr,
+    path::{Path, PathBuf},
+    sync::Arc,
+};
+use util::paths::CONVERSATIONS_DIR;
+
+#[derive(Serialize, Deserialize)]
+pub struct SavedMessage {
+    pub id: MessageId,
+    pub start: usize,
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct SavedConversation {
+    pub id: Option<String>,
+    pub zed: String,
+    pub version: String,
+    pub text: String,
+    pub messages: Vec<SavedMessage>,
+    pub message_metadata: HashMap<MessageId, MessageMetadata>,
+    pub summary: String,
+}
+
+impl SavedConversation {
+    pub const VERSION: &'static str = "0.2.0";
+
+    pub async fn load(path: &Path, fs: &dyn Fs) -> Result<Self> {
+        let saved_conversation = fs.load(path).await?;
+        let saved_conversation_json =
+            serde_json::from_str::<serde_json::Value>(&saved_conversation)?;
+        match saved_conversation_json
+            .get("version")
+            .ok_or_else(|| anyhow!("version not found"))?
+        {
+            serde_json::Value::String(version) => match version.as_str() {
+                Self::VERSION => Ok(serde_json::from_value::<Self>(saved_conversation_json)?),
+                "0.1.0" => {
+                    let saved_conversation =
+                        serde_json::from_value::<SavedConversationV0_1_0>(saved_conversation_json)?;
+                    Ok(Self {
+                        id: saved_conversation.id,
+                        zed: saved_conversation.zed,
+                        version: saved_conversation.version,
+                        text: saved_conversation.text,
+                        messages: saved_conversation.messages,
+                        message_metadata: saved_conversation.message_metadata,
+                        summary: saved_conversation.summary,
+                    })
+                }
+                _ => Err(anyhow!(
+                    "unrecognized saved conversation version: {}",
+                    version
+                )),
+            },
+            _ => Err(anyhow!("version not found on saved conversation")),
+        }
+    }
+}
+
+#[derive(Serialize, Deserialize)]
+struct SavedConversationV0_1_0 {
+    id: Option<String>,
+    zed: String,
+    version: String,
+    text: String,
+    messages: Vec<SavedMessage>,
+    message_metadata: HashMap<MessageId, MessageMetadata>,
+    summary: String,
+    api_url: Option<String>,
+    model: OpenAiModel,
+}
+
+pub struct SavedConversationMetadata {
+    pub title: String,
+    pub path: PathBuf,
+    pub mtime: chrono::DateTime<chrono::Local>,
+}
+
+impl SavedConversationMetadata {
+    pub async fn list(fs: Arc<dyn Fs>) -> Result<Vec<Self>> {
+        fs.create_dir(&CONVERSATIONS_DIR).await?;
+
+        let mut paths = fs.read_dir(&CONVERSATIONS_DIR).await?;
+        let mut conversations = Vec::<SavedConversationMetadata>::new();
+        while let Some(path) = paths.next().await {
+            let path = path?;
+            if path.extension() != Some(OsStr::new("json")) {
+                continue;
+            }
+
+            let pattern = r" - \d+.zed.json$";
+            let re = Regex::new(pattern).unwrap();
+
+            let metadata = fs.metadata(&path).await?;
+            if let Some((file_name, metadata)) = path
+                .file_name()
+                .and_then(|name| name.to_str())
+                .zip(metadata)
+            {
+                let title = re.replace(file_name, "");
+                conversations.push(Self {
+                    title: title.into_owned(),
+                    path,
+                    mtime: metadata.mtime.into(),
+                });
+            }
+        }
+        conversations.sort_unstable_by_key(|conversation| Reverse(conversation.mtime));
+
+        Ok(conversations)
+    }
+}