17.0 migr mail show follower

[thomaspot]

a) Migrated module mail_show_follower to Odoo v17
b) Added 2 extra options in settings to be able to choose font and background color

[pedrobaeza]

Thanks for the contribution.

Please preserve commit history following technical method explained in https://github.com/OCA/maintainer-tools/wiki/Migration-to-version-17.0.

If the jump is between several versions, you have to modify the source branch in the main command to accommodate it to this circumstance.

[github-actions]

There hasn't been any activity on this pull request in the past 4 months, so it has been marked as stale and it will be closed automatically if no further activity occurs in the next 30 days.
If you want this PR to never become stale, please ask a PSC member to apply the "no stale" label.