ai: fix startup to allow 0 price on ai models

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What does this pull request do? Explain your changes. (required)

Update model config parsing so price of 0 is allowed. Mainly geared toward helping testing with no deposit/reserve running a full Gateway and Orchestrator stack.

Specific updates (required)

• Changed model config parsing to allow price of 0.

How did you test each of these updates (required)

Does this pull request close any open issues?

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 31.97154%. Comparing base (e52c907) to head (882cc79).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
cmd/livepeer/starter/starter.go	0.00000%	1 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3674         +/-   ##
===================================================
- Coverage   31.97365%   31.97154%   -0.00211%     
===================================================
  Files            156         156                 
  Lines          47364       47364                 
===================================================
- Hits           15144       15143          -1     
- Misses         31326       31327          +1     
  Partials         894         894                 

Files with missing lines	Coverage Δ
cmd/livepeer/starter/starter.go	7.28155% <0.00000%> (ø)

... and 1 file with indirect coverage changes

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Files with missing lines	Coverage Δ
cmd/livepeer/starter/starter.go	7.28155% <0.00000%> (ø)

... and 1 file with indirect coverage changes

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[eliteprox]

lgtm, did not find any issues downstream with 0 price. We've been using this in testing for the past few weeks with no issues