obs-webrtc: Add 512Kb limit for WHIP Responses

[Sean-Der]

Description

Add a 512Kb limit on HTTP Responses from WHIP servers.

Motivation and Context

Fail earlier before we pass into libdatachannel.

How Has This Been Tested?

Tested against https://b.siobud.com so happy case still works.

Ran broadcast box locally and added lots of padding and confirmed error handling works.

Types of changes

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

Checklist:

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