feat: OCI authentication sidecar

[maciaszczykm]

Test Plan

• AWS - tested with region, key ID and secret auth, then also with assume role, used result token to login to the registry from CLI
• Azure - tested with client secret auth, used result token to upload image to the registry from CLI
• GCP - tested with app credentials
• Basic - tested with username and password

Checklist

• If required, I have updated the Plural documentation accordingly.
• I have added tests to cover my changes.
• I have added a meaningful title and summary to convey the impact of this PR to a user.

[linear]

PROD-2497 OCI authentication sidecar

[michaeljguarino]

We probably want a health check endpoint on here too (would need to be unauthed)

[maciaszczykm]

Added /health endpoint.

[michaeljguarino]

This struct has all the needed json tags right?

[maciaszczykm]

Yes:

// AuthConfig contains authorization information for connecting to a Registry
// Inlined what we use from github.com/docker/cli/cli/config/types
type AuthConfig struct {
	Username string `json:"username,omitempty"`
	Password string `json:"password,omitempty"`
	Auth     string `json:"auth,omitempty"`

	// IdentityToken is used to authenticate the user and get
	// an access token for the registry.
	IdentityToken string `json:"identitytoken,omitempty"`

	// RegistryToken is a bearer token to be sent to a registry
	RegistryToken string `json:"registrytoken,omitempty"`
}