Add push targets feature to rebroadcast a path

[aniolpages]

This PR adds push targets to paths.

A push target allows MediaMTX to republish a path to an external destination, with runtime status exposed through the API. Push targets can be defined statically in path configuration and can also be managed dynamically through new API endpoints.

Supported target protocols:

• RTMP
• RTMPS
• RTSP
• RTSPS
• SRT

Path-level push target support
Added a new pushTargets path option.

This allows configuring one or more outbound destinations directly in a path configuration, for example:

paths:
  mypath:
    pushTargets:
      - url: rtmp://example.com/live/stream
      - url: rtmps://example.com/live/stream

At startup, configured targets are created automatically and tied to the path.

Runtime API for push targets
Added new API endpoints to list, inspect, add, and remove push targets for a path:

GET /v3/paths/pushtargets/list/pathName

GET /v3/paths/pushtargets/get/pathName/targetId

POST /v3/paths/pushtargets/add/pathName

{
  "url":"rtsp://example.com/stream"
}

DELETE /v3/paths/pushtargets/remove/pathname/targetId

[aler9]

This, if correctly implemented, would fix #4273

[codecov]

Codecov Report

❌ Patch coverage is 17.44841% with 880 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.38%. Comparing base (184899d) to head (f8f9451).
⚠️ Report is 33 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/push/target.go	2.40%	649 Missing ⚠️
internal/api/api_pushtargets.go	23.44%	91 Missing and 20 partials ⚠️
internal/push/manager.go	0.00%	66 Missing ⚠️
internal/core/path.go	72.64%	26 Missing and 6 partials ⚠️
internal/core/path_manager.go	67.34%	12 Missing and 4 partials ⚠️
internal/conf/push_target.go	66.66%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5558      +/-   ##
==========================================
- Coverage   60.87%   58.38%   -2.49%     
==========================================
  Files         200      204       +4     
  Lines       16865    17931    +1066     
==========================================
+ Hits        10266    10469     +203     
- Misses       5727     6563     +836     
- Partials      872      899      +27     

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