Add custom PostUpdateHook for sbt-typelevel

[armanbilge]

This adds a custom PostUpdateHook for sbt-typelevel, which calls a tlPrePrBotHook command alias. The idea is that:

1. Since sbt-typelevel subsumes several other plugins, it may require multiple post-update steps to be run.
2. We can easily update the command in sbt-typelevel without needing to change Scala Steward.
3. Downstream plugins can update the alias with their own custom steps, without needing to add their own PostUpdateHook to Steward.

Additional background in:

• Add tlPrePrBotHook typelevel/sbt-typelevel#111.

Let me know what you think. Thanks in advance! :)

[armanbilge]

sbt-typelevel-ci-release is a lower-level plugin which only needs the sbt-github-actions post-update step.

[codecov]

Codecov Report

Merging #2492 (c82d7d2) into main (510db32) will decrease coverage by 0.05%.
The diff coverage is 72.72%.

@@            Coverage Diff             @@
##             main    #2492      +/-   ##
==========================================
- Coverage   81.19%   81.14%   -0.06%     
==========================================
  Files         142      142              
  Lines        2489     2498       +9     
  Branches       55       44      -11     
==========================================
+ Hits         2021     2027       +6     
- Misses        468      471       +3     

Impacted Files	Coverage Δ
...rg/scalasteward/core/edit/hooks/HookExecutor.scala	89.65% <72.72%> (-4.23%)	⬇️

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[fthomas]

LGTM

[mzuehlke]

@armanbilge In case you didn't know since #2434 Scala Steward can have repo specific post update hooks.
But each user of the sbt-typelevel plugin would have to add them herself/himself.

See: https://github.com/scala-steward-org/scala-steward/blob/main/docs/repo-specific-configuration.md

[armanbilge]

@mzuehlke thanks, that config works well for single repositories but is difficult to maintain across orgs.

For example, sbt-http4s-org extends sbt-typelevel and would like to add its own customized post-update hooks for all the repositories in http4s org. With these changes, all it needs to do is update the tlPrePrBotHook command alias with its own commands.