Add opt-out settings for email notifications

[mikkonie]

Following bihealth/sodar-core#1417, we should also add similar opt-out settings for landing zone and samplesheet activities.

Tasks

• [x] Add opt-out for iRODS data request accept/reject
• [x] Add opt-out for landing zone owner status updates
• [x] Update tests (see also #1916)
• [x] Update user profile and major changes docs

[mikkonie]

Done.