feat: configure keria with environment variables

[lenkan]

• Move all access to os.getenv to start.py to make it easier to get an overview of what environment variables are available.
  • Previous ones were KERI_AGENT_CORS and KERIA_RELEASER_TIMEOUT
• Added KERIA_CURLS which is the endpoint for the "KERI port". Since this is dependent on the deployment, it is convenient to be able to configure this with an environment variable.
• Added KERIA_DURLS and KERIA_IURLS, to be able to configure "default" witnesses and data urls for agents.
• Removed the default docker entrypoint that sets up "demo-witness-oobis". From what I could see, this file is not copied into the image anyway.

Closes #326

[codecov]

Codecov Report

Attention: Patch coverage is 98.36066% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.82%. Comparing base (18d3ad7) to head (53757b6).
Report is 40 commits behind head on main.

Files with missing lines	Patch %	Lines
src/keria/app/agenting.py	96.42%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #333      +/-   ##
==========================================
+ Coverage   93.06%   93.82%   +0.75%     
==========================================
  Files          36       36              
  Lines        7121     8076     +955     
==========================================
+ Hits         6627     7577     +950     
- Misses        494      499       +5     

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[iFergal]

LGTM!

[2byrds]

LGTM