rtmp: Add warning for bitrate enforcement with stream encoder

[mohidd]

When 'Use stream encoder' is enabled, OBS silently enforces streaming service bitrate limits during recording. This commit adds warnings to notify users of this behavior, improving clarity.

Description

This change introduces user-facing warnings to clarify when "Use stream encoder" enforces bitrate limits during recording.

Added warnings in init_send to notify users if the recording bitrate is constrained by streaming service settings.
Added warnings in dbr_set_bitrate to notify users when dynamic bitrate is adjusted during streaming due to network conditions.
These changes improve user awareness and reduce confusion about quality degradation when "Use stream encoder" is enabled.

Motivation and Context

Currently, when "Use stream encoder" is enabled, OBS silently adjusts the recording bitrate to conform to streaming service limitations. Users are not notified about this behavior, which can lead to unexpected recording quality issues. This change resolves the lack of feedback by notifying users when their bitrate is adjusted, providing transparency.

This addresses an issue commonly reported by users and contributes to a better user experience.

#10878

How Has This Been Tested?

Verified warnings appear in the OBS log when recording bitrate is constrained by streaming service settings.
Simulated dynamic bitrate adjustments during streaming and confirmed the warnings appear as expected.
Tested on Windows 10 (x64) using OBS version 30.1.2.
Ran tests with both single-track and multi-track audio/video encoders.

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[derrod]

This PR is probably violating our AI and machine learning policy given that it is complete and utter nonsense, in the wrong part of the codebase, using hallucinated functions.