Added docs for data sources

docusaurus/docs/data_repository_permissions_groups.md

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+---
+id: data_repository_permissions_groups
+title: bitbucketserver_repository_permissions_groups
+---
+
+Retrieve a list of groups that have been granted at least one repository level permission to the specified repo.
+
+## Example Usage
+
+```
+data "bitbucketserver_repository_permissions_groups" "my-repo-groups" {
+  project    = "TEST"
+  repository = "my-repo"
+}
+```
+
+### Applying a Custom Filter
+
+Find project groups starting with `dev` with project permissions.
+ 
+```
+data "bitbucketserver_repository_permissions_groups" "my-repo-dev-groups" {
+  project = "TEST"
+  repository = "my-repo"
+  filter  = "dev"
+}
+```
+
+## Argument Reference
+
+* `project` - Required. Project Key to lookup permissions for.
+* `repository` - Required. Repository slug to lookup permissions for.
+* `filter` - Optional. If specified only group names containing the supplied string will be returned.
+
+## Attribute Reference
+
+* `groups` - List of maps containing `name` and `permission` keys. Available permissions are:
+
+    * `REPO_READ`
+    * `REPO_WRITE`
+    * `REPO_ADMIN`