Add retry logic for failures during import

As part of our short term effort to improve imports &1810 (closed) as explained in #39100 (closed)

We have some intermittent failures during import when accessing internal services, like Gitaly, DB.

This MR introduces retry mechanism for following exceptions:

• ActiveRecord::StatementInvalid: Superclass for all database execution errors.
• GRPC::DeadlineExceeded: Gitaly timeout

It will retry only on relation.save!, with intent of trying this at most 3 times.

Total number of retries, final retry status and exception details are stored in ImportFailure.

If retry succeed, retried status is set to success, otherwise we set status to failed

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides

Availability and Testing

This change should have very little impact on performance of the application, but it should make import more reliable.

Relates #39100 (closed)