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/zed/Cargo.toml

@@ -71,7 +71,6 @@ recent_projects.workspace = true
 release_channel.workspace = true
 rope.workspace = true
 search.workspace = true
-semantic_index.workspace = true
 serde.workspace = true
 serde_json.workspace = true
 settings.workspace = true

crates/zed/src/main.rs

@@ -174,7 +174,7 @@ fn main() {
             node_runtime.clone(),
             cx,
         );
-        assistant::init(cx);
+        assistant::init(client.clone(), cx);
 
         extension::init(
             fs.clone(),
@@ -247,7 +247,6 @@ fn main() {
         tasks_ui::init(cx);
         channel::init(&client, user_store.clone(), cx);
         search::init(cx);
-        semantic_index::init(fs.clone(), http.clone(), languages.clone(), cx);
         vim::init(cx);
         terminal_view::init(cx);
 

crates/zed/src/zed.rs

@@ -3060,7 +3060,7 @@ mod tests {
             collab_ui::init(&app_state, cx);
             project_panel::init((), cx);
             terminal_view::init(cx);
-            assistant::init(cx);
+            assistant::init(app_state.client.clone(), cx);
             initialize_workspace(app_state.clone(), cx);
             app_state
         })