Stop caching repository branch_names with cache_method_as_redis_set

What does this MR do and why?

This MR introduces a feature flag mechanism to conditionally disable Redis caching for the branch_names method in the Repository model.

• Adds a new feature flag avoid_branch_names_cache that allows bypassing the Redis cache for repository branch names.
• Modifies the cache_method_as_redis_set method in RepositoryCacheAdapter to accept an avoid_cache parameter that can conditionally skip caching.
• When the feature flag is enabled, branch_names calls go directly to the raw repository instead of using the Redis cache.
• Updates both the main branch_names method and the branch_names_include? helper method to respect the cache bypass.

References

• https://gitlab.com/gitlab-org/gitlab/-/issues/525991+

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Related to #569853 (closed)