Optionally delete lock files after X attempts

[ChristopherRabotin]

High level description

In CI, when the tests are aborted, the metaload may have been in the middle of downloading a file. In those cases, the lock file persists. This persisting should be optional so that the user can control whether or not to delete the lock files after X attempts.

Requirements

• Add an optional param to delete the lock files
• Add the number of retries as a parameter

These both affect mostly the Python interface, but should be reflected in the Rust library somehow.

Test plans

• Manually create a lock file in the tests and make sure that Metaload deletes it.