fix(dav): Parse sender PARTSTAT in REPLYs

[miaulalala]

• Resolves: Parse the ATTENDEE PARTSTAT for the "REPLY" event invitation email #36554

Summary

Parse the PARTSTAT of the sender if the iMIP method is REPLY. Will make iMIP emails more fancy and tell the recipient if the attendee has accepted, declined or tentatively accepted in the mail itself:

Before	After

(Strings need to be translated yet)

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[miaulalala]

/backport to stable26

[tcitworld]

Nice improvement!

[fabricemous]

Seen it and I think this is best sentence to use

stale