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/Cargo.toml

@@ -5,17 +5,14 @@ edition = "2021"
 publish = false
 license = "GPL-3.0-or-later"
 
-[lints]
-workspace = true
-
 [lib]
 path = "src/assistant.rs"
 doctest = false
 
 [dependencies]
-ai.workspace = true
 anyhow.workspace = true
 chrono.workspace = true
+client.workspace = true
 collections.workspace = true
 editor.workspace = true
 fs.workspace = true
@@ -26,12 +23,13 @@ language.workspace = true
 log.workspace = true
 menu.workspace = true
 multi_buffer.workspace = true
+open_ai = { workspace = true, features = ["schemars"] }
 ordered-float.workspace = true
+parking_lot.workspace = true
 project.workspace = true
 regex.workspace = true
 schemars.workspace = true
 search.workspace = true
-semantic_index.workspace = true
 serde.workspace = true
 serde_json.workspace = true
 settings.workspace = true
@@ -45,7 +43,6 @@ uuid.workspace = true
 workspace.workspace = true
 
 [dev-dependencies]
-ai = { workspace = true, features = ["test-support"] }
 ctor.workspace = true
 editor = { workspace = true, features = ["test-support"] }
 env_logger.workspace = true