rtmp-services: Add Bitmovin

[CMThF]

Description

Added an rtmp service for Bitmovin.

Motivation and Context

Add Bitmovin live streaming to the common rtmp services.
Bitmovin is a leading provider of video software and cloud infrastructure for online media companies and enterprises globally.

I already created a PR once, where I tried to implement the generic workflow of Bitmovin. Back then, Bitmovin did not offer a single ingest point with stream-key, so it was a bit more complicated to authenticate, create a stream, fetch the metadata and input to it.
Bitmovin heard OBS' feedback, and introduced a simplified workflow, named Bitmovin Streams - featuring the common practice of a single ingest point with stream key.

How Has This Been Tested?

• JSON validation
• manual test
  • Build OBS
  • check if Bitmovin option is in the rtmp services dropdown menu
  • select it
  • start a Bitmovin Streams Live stream via the dashboard
  • copy stream key and configure it in OBS
  • start ingest
  • watch stream in the Bitmovin preview player

Types of changes

• New feature (non-breaking change which adds functionality)

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.