Draft: Allow RuboCop to inspect erb files

What does this MR do and why?

This MR adds rubocop-erb so RuboCop can now inspect ERB files 🎉

Offenses

114  Style/FormatString
4    Layout/SpaceInsideBlockBraces
2    Layout/SpaceBeforeBlockBraces
2    Style/RedundantInterpolation
2    Style/StringConcatenation
1    Style/RedundantCondition
--
125  Total in 56 files

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.