Use database for github creds

Add database models that deal with github credentials. This change
adds models for github endpoints (github.com, GHES, etc). This change
also adds code to migrate config credntials to the DB.

Tests need to be fixed and new tests need to be written. This will come
in a later commit.

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

config/config.go

@@ -241,6 +241,14 @@ type GithubApp struct {
 	InstallationID int64  `toml:"installation_id" json:"installation-id"`
 }
 
+func (a *GithubApp) PrivateKeyBytes() ([]byte, error) {
+	keyBytes, err := os.ReadFile(a.PrivateKeyPath)
+	if err != nil {
+		return nil, fmt.Errorf("reading private_key_path: %w", err)
+	}
+	return keyBytes, nil
+}
+
 func (a *GithubApp) Validate() error {
 	if a.AppID == 0 {
 		return fmt.Errorf("missing app_id")
@@ -472,6 +480,11 @@ type Database struct {
 	// Don't lose or change this. It will invalidate all encrypted data
 	// in the DB. This field must be set and must be exactly 32 characters.
 	Passphrase string `toml:"passphrase"`
+
+	// MigrateCredentials is a list of github credentials that need to be migrated
+	// from the config file to the database. This field will be removed once GARM
+	// reaches version 0.2.x. It's only meant to be used for the migration process.
+	MigrateCredentials []Github `toml:"-"`
 }
 
 // GormParams returns the database type and connection URI