[Backport fc-26.05-dev] jitsi: fix and cleanup role

[platform-pr-manager]

Bot-based backport to fc-26.05-dev, triggered by a label in #2118. Original body:

Remove vendored upstream modules while still using our watchdog mechanism. This also fixes the problems we had with prosody.

PL-135075

@flyingcircusio/release-managers

Release process

• Created changelog entry using ./changelog.sh

PR release workflow (internal)

• PR has internal ticket
• internal issue ID (PL-…) part of branch name
• internal issue ID mentioned in PR description text
• ticket is on Platform agile board
• if ticket is more urgent than within the next few days, directly contact a member of the Platform team

• set urgency and risk labels
• ensure the merge bot has determined a merge date
• ensure all checks are green
• get a review from a colleague

Design notes

• Provide a feature toggle if the change might need to be adjusted/reverted quickly depending on context. Consider whether the default should be on or off. Example: rate limiting.
• All customer-facing features and (NixOS) options need to be discoverable from documentation. Add or update relevant documentation such that hosted and guided customers can understand it as well.

Security implications

• Security requirements defined? (WHERE)
  • not more attack surface than before
• Security requirements tested? (EVIDENCE)
  • tested on test machine
  • currently no automated test (see PL-134009)