[EASI-4614] Initial email work for GRB Discussions

[downeyn-cms]

EASI-4614 EASI-4638 EASI-4645 EASI-4646

Description

• Initial work for the emails generated by the upcoming GRB review discussion functionality
• Added templates and handlers for the emails generated by specific actions (replies and tagging)
• This work is not complete yet. as some of the final details are blocked by the discussion functionality (e.g. discussion ID, user names, group names, etc.)

How to test this change

• This is a tough one to test locally, any ideas on how to expand on the testing I already added would be welcome
• Full testing is blocked by implementation of the discussion functionality

PR Author Checklist

• I have provided a detailed description of the changes in this PR.
• I have provided clear instructions on how to test the changes in this PR.
• I have updated tests or written new tests as appropriate in this PR.

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[mynar7]

Could you add these new emails to the email script file?

Also discussion content is going to be HTML so we can update these emails to use that model instead of strings.