Ban .keys.first and .values.first

What does this MR do?

Add cop as suggested by issue #30349 (closed) .keys.first and .values.first is memory and time consuming, we suggest to use .each_key.first and .each_value.first (or .first.first and .first.second)

This MR:

• Add a robucop cop to check .keys.first and .values.first. It also auto-correct: .keys.first => each_key.first, .values.first => .each_value.first
• Fixed the occurrences in existing files

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content