assistant: Add Bedrock support (#21092)

Closes #16544

Release Notes:

- Added support for AWS Bedrock to the Assistant.

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>
Co-authored-by: Anthony <anthony@zed.dev>
Co-authored-by: Anthony Eid <hello@anthonyeid.me>

crates/assistant_settings/src/assistant_settings.rs

@@ -359,6 +359,7 @@ fn providers_schema(_: &mut schemars::gen::SchemaGenerator) -> schemars::schema:
     schemars::schema::SchemaObject {
         enum_values: Some(vec![
             "anthropic".into(),
+            "bedrock".into(),
             "google".into(),
             "lmstudio".into(),
             "ollama".into(),