Draft: Add RuboCop rule RSpec/SpecHelperTag

What does this MR do and why?

This rule tags spec with helper: :fast_spec if a spec require fast_spec_helper. Otherwise it will remove this tag.

This might be useful to group specs with knapsack.

Refs #350700 (comment 1067272389)

Example

$ be rubocop --only RSpec/SpecHelperTag spec/haml_lint/linter/no_plain_nodes_spec.rb
Inspecting 1 file
C

Offenses:

spec/haml_lint/linter/no_plain_nodes_spec.rb:9:1: C: RSpec/SpecHelperTag: Add spec tag helper: :fast_spec.
RSpec.describe HamlLint::Linter::NoPlainNodes do ...
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected, 1 offense auto-correctable

Draft?

• Add auto-correction to fix specs
• [-] Add development guidelines

How to set up and validate locally

bin/rake rubocop:todo:generate[RSpec/SpecHelperTag]

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.