Add simple instance-wide PR throttle

[fthomas]

This adds a simple instance-wide PR throttle. It can be activated by adding the --pr-throttle-skip=$duration or --pr-throttle-wait=$duration command-line options. With --pr-throttle-skip=$duration Scala Steward will skip creating PRs for $duration after the last PR. With --pr-throttle-wait=$duration it actively waits until $duration is elapsed before creating the next PR.

Closes #2934, closes #2355

[armanbilge]

Thank you so much! This strategy is easy to understand and will work well for us 👍

[codecov]

Codecov Report

❌ Patch coverage is 69.44444% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.68%. Comparing base (ef3cd47) to head (1783dd9).
⚠️ Report is 1546 commits behind head on main.

Files with missing lines	Patch %	Lines
...calasteward/core/nurture/PullRequestThrottle.scala	11.11%	8 Missing ⚠️
...org/scalasteward/core/application/StewardAlg.scala	0.00%	2 Missing ⚠️
...ala/org/scalasteward/core/nurture/NurtureAlg.scala	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2970      +/-   ##
==========================================
- Coverage   90.96%   90.68%   -0.28%     
==========================================
  Files         157      159       +2     
  Lines        3209     3253      +44     
  Branches      242      224      -18     
==========================================
+ Hits         2919     2950      +31     
- Misses        290      303      +13     

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[barryoneill]

Hi @fthomas - is there any plan to bring this in?