feat: Separate workspace agent for tests

[kylecarbs]

This adds tests for Google Cloud authentication, and lays
the ground-work for future agent auth types in the future.

[codecov]

Codecov Report

Merging #567 (1cf1805) into main (21fdb80) will increase coverage by 0.15%.
The diff coverage is 63.21%.

@@            Coverage Diff             @@
##             main     #567      +/-   ##
==========================================
+ Coverage   62.92%   63.07%   +0.15%     
==========================================
  Files         194      195       +1     
  Lines       11097    11205     +108     
  Branches       85       85              
==========================================
+ Hits         6983     7068      +85     
- Misses       3358     3373      +15     
- Partials      756      764       +8     

Flag	Coverage Δ
unittest-go-	62.00% <63.21%> (+0.31%)	⬆️
unittest-go-macos-latest	58.01% <63.21%> (+0.70%)	⬆️
unittest-go-ubuntu-latest	61.16% <63.21%> (+0.35%)	⬆️
unittest-go-windows-2022	57.07% <63.21%> (+0.54%)	⬆️
unittest-js	63.32% <ø> (ø)

Impacted Files	Coverage Δ
cli/ssh.go	5.12% <0.00%> (-1.33%)	⬇️
agent/conn.go	65.38% <65.38%> (ø)
codersdk/workspaceresources.go	59.59% <70.00%> (+1.57%)	⬆️
cli/workspaceagent.go	66.66% <92.59%> (+56.66%)	⬆️
agent/agent.go	67.45% <100.00%> (+0.22%)	⬆️
coderd/coderdtest/coderdtest.go	99.15% <100.00%> (+0.27%)	⬆️
provisionersdk/serve.go	35.13% <0.00%> (-8.11%)	⬇️
provisionersdk/transport.go	74.46% <0.00%> (-4.26%)	⬇️
peer/conn.go	77.15% <0.00%> (-3.05%)	⬇️
provisioner/echo/serve.go	54.40% <0.00%> (-2.40%)	⬇️
... and 7 more

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[coadler]

Missing lots of wraps in this file

[kylecarbs]

Good call. Dunno why I do that 🤦