Add routes to allow git actions on snippet repositories

What does this MR do?

In this MR we implement the following:

• Refactors the git_http routes because, for now, snippet repositories won't support LFS (mainly because lfs_enabled is a project feature and we have to think if we could enable it by default for personal snippets).
• It also updates the GitHttpController(s) and the SSH internal API to allow basic cloning/pushing/pulling operations for resources other than projects.

Refs #39176 (closed) Closes #205666 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

app/controllers/repositories/git_http_client_controller.rb

@@ -6,7 +6,7 @@ class GitHttpClientController < Repositories::ApplicationController
     include KerberosSpnegoHelper
     include Gitlab::Utils::StrongMemoize
 
-    attr_reader :authentication_result, :redirected_path
+    attr_reader :authentication_result, :redirected_path, :container
 
     delegate :actor, :authentication_abilities, to: :authentication_result, allow_nil: true
     delegate :type, to: :authentication_result, allow_nil: true, prefix: :auth_result
@@ -93,7 +93,7 @@ def render_missing_personal_access_token
 
     def repository
       strong_memoize(:repository) do
-        repo_type.repository_for(@container)
+        repo_type.repository_for(container)
       end
     end
 
@@ -117,7 +117,8 @@ def ci?
     def http_download_allowed?
       Gitlab::ProtocolAccess.allowed?('http') &&
       download_request? &&
-      (project && Guest.can?(:download_code, project) || @container.is_a?(PersonalSnippet))
+      container &&
+      Guest.can?(:download_code, container)
     end
   end
 end