gateway: ai authWebhook: send gatewayHost to auth webhook

[gioelecerati]

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

Specific updates (required)

• Set up a gatewayHost flag and add it to livepeernode
• Send the gatewayHost back to the live ai auth webhook

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 14.28571% with 6 lines in your changes missing coverage. Please review.

Project coverage is 33.91978%. Comparing base (df2ed58) to head (288f07e).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
cmd/livepeer/starter/starter.go	0.00000%	5 Missing ⚠️
server/ai_mediaserver.go	0.00000%	1 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3320         +/-   ##
===================================================
- Coverage   33.94992%   33.91978%   -0.03014%     
===================================================
  Files            141         141                 
  Lines          37140       37173         +33     
===================================================
  Hits           12609       12609                 
- Misses         23811       23844         +33     
  Partials         720         720                 

Files with missing lines	Coverage Δ
cmd/livepeer/livepeer.go	55.65217% <100.00000%> (+0.19365%)	⬆️
core/livepeernode.go	74.01575% <ø> (ø)
server/auth.go	63.72549% <ø> (ø)
server/ai_mediaserver.go	7.90514% <0.00000%> (-0.01565%)	⬇️
cmd/livepeer/starter/starter.go	7.51409% <0.00000%> (-0.02360%)	⬇️

... and 1 file with indirect coverage changes

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Files with missing lines	Coverage Δ
cmd/livepeer/livepeer.go	55.65217% <100.00000%> (+0.19365%)	⬆️
core/livepeernode.go	74.01575% <ø> (ø)
server/auth.go	63.72549% <ø> (ø)
server/ai_mediaserver.go	7.90514% <0.00000%> (-0.01565%)	⬇️
cmd/livepeer/starter/starter.go	7.51409% <0.00000%> (-0.02360%)	⬇️

... and 1 file with indirect coverage changes