fix: misc issues for cloud editing

[AdityaHegde]

1. Publish button disabled when there are no local changes but current branch is different. We will need the API that gets the diff between 2 branches before we disable this.
2. Additional spinner on connector selector. We can offload this in welcome page so that it is loaded in the background.
3. .env fetch is attempted even if it doesnt exist. Because of file watcher we should already know if it exists or not.
4. PushEnv when we delete env entries during connector/source deletion.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!