[cli,lock] Allow wait_for_lock

[Wheest]

If we are running multiple instances of DVC in parallel in the same repo, commands can crash because they can't acquire a lock.

This is reasonable in most use-cases, but I've been using DVC in my bazel pipelines, which runs jobs in parallel. Therefore, I've added a --wait-for-lock flag that allows a process to be more patient.

Note this is my first PR, so I may not be following all the conventions of the project. Feedback appreciated!

Fixes #2520

[codecov]

Codecov Report

Attention: Patch coverage is 89.04110% with 8 lines in your changes missing coverage. Please review.

Project coverage is 91.08%. Comparing base (2431ec6) to head (711e5ee).
Report is 72 commits behind head on main.

Files with missing lines	Patch %	Lines
dvc/lock.py	78.57%	6 Missing ⚠️
tests/func/test_lock.py	95.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10784      +/-   ##
==========================================
+ Coverage   90.68%   91.08%   +0.40%     
==========================================
  Files         504      504              
  Lines       39795    40227     +432     
  Branches     3141     3179      +38     
==========================================
+ Hits        36087    36640     +553     
+ Misses       3042     2958      -84     
+ Partials      666      629      -37     

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[skshetry]

Thank you for contributing.

Just so you are aware, there are two kinds of lock in dvc: 1) .dvc/lock that prevents another dvc process from running that could change repository, and 2) there's rwlock that is a more specific lock for specific dependencies and outputs (see Internal Directories and Files.

Although this adds wait for the first kind of lock, you may still run into rwlock if you try to change the same dependencies/outputs from different DVC processes.

[Wheest]

Many thanks, cheers! I'll need to see if this influences my use-cases when running bazel