start working on letsencrypt cert handling

internal/config/letsencrypt.go

@@ -0,0 +1,11 @@
+package config
+
+// LetsEncryptConfig wraps everything needed to manage letsencrypt certificates from within gotosocial.
+type LetsEncryptConfig struct {
+	// Should letsencrypt certificate fetching be enabled?
+	Enabled bool
+	// Where should certificates be stored?
+	CertDir string
+	// Email address to pass to letsencrypt for notifications about certificate expiry etc.
+	EmailAddress string
+}