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

* Port to GitHub actions

* Fix

* Make docs terraform registry compatible

docs/data-sources/bitbucketserver_user.md

@@ -0,0 +1,21 @@
+# Data Source: bitbucketserver_user
+
+This data source allows you to retrieve Bitbucket user details.
+
+## Example Usage
+
+```hcl
+data "bitbucketserver_user" "admin" {
+  name = "admin"
+}
+```
+
+## Argument Reference
+
+* `name` - Unique name of the user.
+
+## Attribute Reference
+
+* `email_address` - User's email.
+* `display_name` - User's display name.
+* `user_id` - User's ID.