Add sanitization to BranchNamer::DependencyGroupStrategy

[TomNaessens]

Summary

This MR adds sanitisation support to the BranchNamer::DependencyGroupStrategy. It addresses this fixme:

dependabot-core/common/lib/dependabot/pull_request_creator/branch_namer/dependency_group_strategy.rb

Line 18 in 0193c77

# FIXME: Incorporate max_length truncation once we allow user config

History

• A max_length option was added to the (at the time) single branch namer: Add max length option to BranchNamer #5338 so users with restrictive branch names (e.g. sometimes found on Gitlab) could limit branch name length
• Introduce group rule to branch namer #6784 split the single branch namer into a solo strategy and a group rule strategy (now the dependency group strategy)
  • This made no use of the max_length parameter
• In [Updater] Wire up and flesh out branch naming for Grouped Update PRs #7084 a comment was added to explain why there was no sanitization included yet

Reasoning

• Although the max_length feature isn't exposed yet on Github, other users downstream are already using the max_length parameter (e.g. through dependabot-gitlab which is built on dependabot-common)
• As we're still creating branches, the normal sanitization should happen, no matter which strategy is used:
  • Branches can always be too long
  • Branches should always follow git ref limitations
  • Characters in branch names should always be able to be restricted (e.g. through the seperator command)
• In the DependencyGroupStrategy, special care is taken that dependency order and time yields a consistent name. As hashing a consistent string also yields a consistent string, it is safe to reuse the sanitization strategy from the SoloStrategy.

To address those, I created a common superclass (BranchNamer::Base) with some basic sanitization methods (at the moment, moved from the SoloStrategy).

[brrygrdn]

Thanks for this, this looks good to me!