Expose the authorized keys tmate feature (#18)

* Expose the authorized keys tmate feature
Described here: https://tmate.io/ in "Access Control"
The variable accepts the file content in raw format (with \n) and dumps it into a file which tmate reads
* Use echo instead of printf
* Add missing quote
* Only setup tmate settings if debug is activated

engine/compiler/compiler.go

@@ -56,12 +56,13 @@ type Resources struct {
 
 // Tmate defines tmate settings.
 type Tmate struct {
-	Image   string
-	Enabled bool
-	Server  string
-	Port    string
-	RSA     string
-	ED25519 string
+	Image          string
+	Enabled        bool
+	Server         string
+	Port           string
+	RSA            string
+	ED25519        string
+	AuthorizedKeys string
 }
 
 // Compiler compiles the Yaml configuration file to an
@@ -247,6 +248,10 @@ func (c *Compiler) Compile(ctx context.Context, args runtime.CompilerArgs) runti
 		envs["DRONE_TMATE_PORT"] = c.Tmate.Port
 		envs["DRONE_TMATE_FINGERPRINT_RSA"] = c.Tmate.RSA
 		envs["DRONE_TMATE_FINGERPRINT_ED25519"] = c.Tmate.ED25519
+
+		if c.Tmate.AuthorizedKeys != "" {
+			envs["DRONE_TMATE_AUTHORIZED_KEYS"] = c.Tmate.AuthorizedKeys
+		}
 	}
 
 	// create the .netrc environment variables if not