#5858 add FlowCrypt secure messaging options in Gmail's actions menu

[martgil]

This PR add's secure compose's messaging options within Gmail's action menu.

Screenshot:

close #5858

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Tests (delete all except exactly one):

• Tests added or updated

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[martgil]

Here is the short demo of the proposed changes of this PR:

Screencast.from.2024-11-23.15-44-54.webm