Revisit fallback URL logic/decision

Created by: erzhtor

Context

After fallback URL changes:

• Released PRs
  • https://github.com/sourcegraph/sourcegraph/pull/25185
  • https://github.com/sourcegraph/sourcegraph/pull/26007
• Not released PRs
  • https://github.com/sourcegraph/sourcegraph/pull/26163
  • https://github.com/sourcegraph/sourcegraph/pull/26258
  • https://github.com/sourcegraph/sourcegraph/pull/26352
  • https://github.com/sourcegraph/sourcegraph/pull/26489

We have a bug that browser extension accidentally uses cloud URL for private repos, breaking code-intel for private repos. We were planning to address this issue, but this brought up a discussion that some enterprise users on self-hosted instances might not want automatic fallback to the cloud at all.

Next steps

• Revert merged changes to main to unblock the main branch from future releases. Close not merged PRs. https://github.com/sourcegraph/sourcegraph/pull/26516
• Lessons learned
  • Why did it happen?
  • What are the consequences?
  • How to prevent it in the future? Lessons
• Revisit decision on the fallback URL logic & design