This commit:
- Implements multi-threaded DuoChat integration
- Updates all GraphQL queries required for the multi-threaded architecture.
- Ensures seamless fallback to single-threaded mode when duo_chat_multi_thread is disabled.
It was initially merged in:
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/179708


Reverted to some breaking-changes in the API
that are resolved.

EE: true

Merged-by: Jannik Lehmann <jlehmann@gitlab.com>
Approved-by: Lindsey Shelton <lshelton@gitlab.com>
Approved-by: Andrew Fontaine <afontaine@gitlab.com>
Reviewed-by: Andrew Fontaine <afontaine@gitlab.com>
Reviewed-by: Jannik Lehmann <jlehmann@gitlab.com>

This update includes the removal of BCollapse component,
which removes supports for `GlCollapseToggleDirective`
and `@hide/@show` event. This MR refactors existing usage
of those in this codebase.

This MR also removes expandable_section.vue, which is no
longer being used.

This reverts merge request !179708

- Implements multi-threaded DuoChat integration
- Updates all GraphQL queries required for the multi-threaded architecture.
- Ensures seamless fallback to single-threaded mode when duo_chat_multi_thread is disabled.

EE: true

When working with storybook locally, if you have to stop and restart it
frequently the prompt to re-download fixtures is a nuisance. This MR
adds an npm script that can be run that will skip the fixtures check
and use the version you already have downloaded.

Set the extensionsHostUrl, workbenchBaseUrl, and embedderOriginUrl
configuration parameters when initializing the Web IDE. Also
remove the baseUrl parameter.

Changelog: changed