Cleanup net-certmanager integration

[ReToCode]

Context

• [Automated] Update net-certmanager nightly #15166
• Archive knative-extensions/net-certmanager community#1563

Proposed Changes

• Follow-up for Integrate net-certmanager in Serving #15066
• Removes specific logging configuration (should be covered by serving controller now)
• Moved config file to ytt instead of third_party (as there is no longer a third_party repo here)
• Removed istio config for webhook that is now part of serving webhook

I did not find more things we might need to update.

/assign @skonto

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ReToCode

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [ReToCode]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.79%. Comparing base (c2d0af1) to head (d46df3e).
Report is 74 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15168      +/-   ##
==========================================
+ Coverage   84.11%   84.79%   +0.67%     
==========================================
  Files         213      218       +5     
  Lines       16783    13469    -3314     
==========================================
- Hits        14117    11421    -2696     
+ Misses       2315     1682     -633     
- Partials      351      366      +15     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[skonto]

Should we start the process for deprecating net-certmanager?

[ReToCode]

Should we start the process for deprecating net-certmanager?

Yes: knative/community#1563, I think I have most. Anything else needed? As per 1.15, we do not need to release it any longer. Docs should be covered in: knative/docs#5804

[skonto]

/lgtm