Add addToExistingLock in E2E test framework

[czarcas7ic]

Background

We recently refactored AddToExistingLock in this PR #1979

As discussed in a call, we should have test coverage on this, and the e2e test suite seems like a good place for this

Suggested Design

• After a lock is created in e2e, add to that existing lock pre upgrade
  • If upgrade is not skipped, after the upgrade, we should attempt to add to the lock that existed pre upgrade as well as a lock that was created post upgrade
  • If upgrade is skipped, just attempt to add to an existing lock that was created
• Ensure the above is done for both superfluid and non superfluid locks

Acceptance Criteria

• design implemented with all tests passing