[15.0][ADD] mail_thread_subject_ignore

[AaronHForgeFlow]

This module allows to avoid fetching mails that are supposed to be automatic replies, this is useful to prevent records like leads, helpdesk tickets, etc to have the chatter full of those automatic replies.

cc @ForgeFlow

[AaronHForgeFlow]

Interesting module mail_autogenerated_header. I understand that the header in those automatic replies is usually properly configured so we can filter them. I will try that one.

[github-actions[bot]]

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.