feat(auth)!: build token implementation

[ecrupper]

Server PR for Epic 1: Build Tokens.

Changes:

• Conversion of router/middleware/token package to router/middleware/auth, which will now only retrieve auth headers from http requests, rather than generate/parse tokens
• Creation of internal/token package, which features a manager that is set up in the context using various new flags added to main.go. In brief, it's a one-stop-shop for token minting and validating and offers configurability to a degree.
• Additional claims added to Claims struct, including information about the token type as well as relevant fields for that token (build tokens have build ids and repo).
• Removal of global permissions for agents
• Worker endpoints used for check in (POST / PUT) have been put behind MustWorker() permissions check, which validates the symmetric token shared between server and worker
• Build/Step/Service/Log update endpoints have been put behind MustBuildAccess() permissions check, which validates the build token, which is provided as a unique auth scope for each build.
• Add GET endpoint for retrieving a build token, which validates the build's status and creates a build token
• Addition of a private key, which will be seeded in the server environment, much like the secret, which will be used to sign and validate all tokens.
• Updates made to MustSecretAdmin which will scope requests with build token auth based on the repo within the token
• Claims will be established in the context for baseAPI endpoints before the user

depends on: go-vela/types#276

waiting for go-vela/types changes to merge in

[codecov]

Codecov Report

Merging #765 (411d800) into main (343d53e) will increase coverage by 0.31%.
The diff coverage is 65.31%.

@@            Coverage Diff             @@
##             main     #765      +/-   ##
==========================================
+ Coverage   54.39%   54.70%   +0.31%     
==========================================
  Files         225      232       +7     
  Lines       16188    16392     +204     
==========================================
+ Hits         8806     8968     +162     
- Misses       6989     7024      +35     
- Partials      393      400       +7     

Impacted Files	Coverage Δ
api/authenticate.go	0.00% <0.00%> (ø)
api/build.go	1.50% <0.00%> (-0.07%)	⬇️
api/secret.go	0.00% <0.00%> (ø)
api/token.go	0.00% <0.00%> (ø)
api/user.go	0.00% <0.00%> (ø)
database/user/table.go	100.00% <ø> (ø)
internal/token/mint.go	57.50% <57.50%> (ø)
internal/token/refresh.go	72.72% <72.72%> (ø)
router/middleware/perm/perm.go	62.33% <78.44%> (+16.12%)	⬆️
internal/token/compose.go	80.43% <80.43%> (ø)
... and 10 more

[jbrockopp]

proposal?

[ecrupper]

proposal?

go-vela/community#755

[jbrockopp]

LGTM