Add a Mappers Hashtag as an option to task comments

[Pseudorandom-Pseudonym]

Is your feature request related to a problem? Please describe.

Sometimes a task has been locked for mapping by many contributors and you want to notify them of your feedback so they may all benefit from it e.g. if the task required a lot of effort so it was locked many times you may want to tell the mappers to split similar tasks in the future.

If a task has been previously invalidated the contributor hashtag is used, then the contributor who invalidated it recieves a notification which is likely not as useful to them.

Describe the solution you'd like

Add a more specific mappers hashtag. This hashtag could perhaps even only notify the mappers who locked a task since the previous (in)validation cycle.

Describe alternatives you've considered

adding @ of each user though this is more manual and error prone.

[linear[bot]]

TECH-860