fix: improve branch name sanitization and creation

[sentry-autofix]

👋 Hi there! This PR was automatically generated by Autofix 🤖

This fix was triggered by Rohan Agarwal

Fixes SEER-J5

• Improves branch name sanitization to handle trailing slashes and empty segments between slashes.
• Adds validation to ensure branch name doesn't end with a slash before creating the branch.
• If the branch name is empty after sanitization, it defaults to "autofix-branch".
• Adds sanitization after adding a random suffix to the branch name to avoid invalid branch names.

If you have any questions or feedback for the Sentry team about this fix, please email autofix@sentry.io with the Run ID: 5770.