LBRY_API env var should be renamed to LBRYNET_API to avoid conflicts

The Issue

Up until lbrynet 0.30 LBRY_API was not parsed (or at least considered) by the SDK, LBRY_API often refers to our internal apis and serveral other projects rely on that environment variable to function.
With lbrynet 0.31, setting LBRY_API to an endpoint different than the default one obviously breaks lbrynet.

Steps to reproduce

1. set LBRY_API to something like https://api.lbry.io
2. try to start lbrynet
3. if lbrynet starts, the API won't work

System Configuration

lbrynet > 0.30

Internal Use

Acceptance Criteria

Definition of Done

• Tested against acceptance criteria
• Tested against the assumptions of user story
• The project builds without errors
• Unit tests are written and passing
• Tests on devices/browsers listed in the issue have passed
• QA performed & issues resolved
• Refactoring completed
• Any configuration or build changes documented
• Documentation updated
• Peer Code Review performed

Search the repository for LBRY_API and the SDK startup or configuration entry points, then identify related tests and documentation. The work is done when the environment-variable references, tests, and documentation consistently use LBRYNET_API and the endpoint behavior is covered.