Recognize the word Time in slash commands so we list all the ones related to time tracking

Description

At the moment, all slash commands about time tracking are not searchable easily. You can type /spend to enter a time spent, but if you've forgotten what this slash command was, it's hard to find it back unless you read the documentation.

Proposal

• Writing /time should list all the available slash commands about time tracking (4 currently)
  • /spend
  • /estimate
  • /remove_estimate
  • /remove_time_spent

Implementation Plan

Adding aliases to these quick actions in lib/gitlab/quick_actions/issue_and_merge_request_actions.rb should do the trick.

We should then add some tests to spec/services/quick_actions/interpret_service_spec.rb