Draft: IDEA: Add macros to notes to include predefined actions/messages

What does this MR do and why?

Many times we have to do repetitive things when working with messages like selecting many labels for your group or approving and assigning reviewer for MRs.

Users can have different set of messages/actions that they are using on daily basis. With this MR I wanted to start a discussion if this is a common problem that we can easily solve.

Idea for MVC:

1. Every user can have different set of macros that are stored for their account in database.
2. When using editor user can apply a macro that will include content defined in database.
3. Users manages macros with GraphQL mutations.
4. Feature is hidden behind feature flag.

Ideas for future improvements:

1. We can store Macros for Instance/Group/Project and users can use them.
2. UI with autocompletion

Screenshots or screen recordings

How to set up and validate locally

1. Go to your Project and open Issue/MR.
2. Try to use /macro welcome_contributor @root or /macro labels_for_my_group
3. Click on Preview or create new Note.

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.