Port to GitHub actions & publish to Terraform registry (#39)

* Port to GitHub actions

* Fix

* Make docs terraform registry compatible

docs/resources/bitbucketserver_mail_server.md

@@ -0,0 +1,33 @@
+# Resource: bitbucketserver_mail_server
+
+Setup mail server configuration.
+
+## Example Usage
+
+```hcl
+resource "bitbucketserver_mail_server" "mail" {
+  hostname       = "mail.example.com"
+  port           = 465
+  protocol       = "SMTPS"
+  sender_address = "bitbucket@example.com"
+}
+```
+
+## Argument Reference
+
+* `hostname` - Required. Hostname of the mail server.
+* `port` - Required. Port number of the mail server. Typically port 25 or 587 for SMTP and 465 for SMTPS.
+* `sender_address` - Required. Email address for notification emails.
+* `protocol` - Optional. SMTP or SMTPS supported. Default `SMTP`
+* `use_start_tls` - Optional. Use SSL/TLS if available. Default `true`
+* `require_start_tls` - Optional. Require SSL to be used. Default `false`
+* `username` - Optional. User to connect with.
+* `password` - Optional. User to connect with.
+
+## Import
+
+Import the existing mail server configuration with the hostname:
+
+```
+terraform import bitbucketserver_mail_server.mail mail.example.com
+```