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/collab/src/api/extensions.rs

@@ -1,6 +1,5 @@
 use crate::{
     db::{ExtensionMetadata, NewExtensionVersion},
-    executor::Executor,
     AppState, Error, Result,
 };
 use anyhow::{anyhow, Context as _};
@@ -136,7 +135,7 @@ async fn download_extension(
 const EXTENSION_FETCH_INTERVAL: Duration = Duration::from_secs(5 * 60);
 const EXTENSION_DOWNLOAD_URL_LIFETIME: Duration = Duration::from_secs(3 * 60);
 
-pub fn fetch_extensions_from_blob_store_periodically(app_state: Arc<AppState>, executor: Executor) {
+pub fn fetch_extensions_from_blob_store_periodically(app_state: Arc<AppState>) {
     let Some(blob_store_client) = app_state.blob_store_client.clone() else {
         log::info!("no blob store client");
         return;
@@ -146,6 +145,7 @@ pub fn fetch_extensions_from_blob_store_periodically(app_state: Arc<AppState>, e
         return;
     };
 
+    let executor = app_state.executor.clone();
     executor.spawn_detached({
         let executor = executor.clone();
         async move {