Wait for all pending requests in Monitor settings feature spec

What does this MR do and why?

This MR attempts to unquarantine a flaky Monitor settings spec (#333665 (closed)). It adds wait_for_all_requests after the "save action".

Although I couldn't reproduce the full issue locally I was able to reproduce some symptoms.

See #333665 (comment 694091528) for more details.

This MR also fixes some (upcoming, currently auto-disabled) RuboCop offenses.

⚠ To future reverter ⚠

To quarantine the flaky spec again, please only revert 5f2e02e74bad3b8620e3337e93654d63749822ef. Thank you ❤

Screenshots or screen recordings

Before	After

How to set up and validate locally

bin/rspec -f d spec/features/projects/settings/monitor_settings_spec.rb

MR acceptance checklist

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