github-release: support specifying a token in the configuration

[XaF]

Follow-up to: #478

For cases where gh is not available, we should support to set a PAT in the configuration.

# Using gh auth token
github:

# Using gh auth token
github:
  auth:
    gh:

# Using gh auth token --hostname xxx
github:
  auth:
    gh:
      hostname: xxx

# Using gh auth token --hostname xxx --user yyy
github:
  auth:
    gh:
      hostname: xxx
      user: yyy

# Using TTT as token
github:
  auth:
    token: TTT