Implement object storage credential (#79)

* Implement credential resource

* Implement test

* Fix test

* Implement data source

* Implement credential acc test

* Add objectstorage credential

* Add test for enableProject

* Add readCredentials test

* Removed unnecessary test case

* Generate docs

* Fix lint

* Fix field name

* Readd credentials group checks

* Fix comment

* Fix comment

* Remove auth

---------

Co-authored-by: Henrique Santos <henrique.santos@freiheit.com>

docs/data-sources/objectstorage_credential.md

@@ -0,0 +1,30 @@
+---
+# generated by https://github.com/hashicorp/terraform-plugin-docs
+page_title: "stackit_objectstorage_credential Data Source - stackit"
+subcategory: ""
+description: |-
+  ObjectStorage credential data source schema.
+---
+
+# stackit_objectstorage_credential (Data Source)
+
+ObjectStorage credential data source schema.
+
+
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `credential_id` (String) The credential ID.
+- `credentials_group_id` (String) The credential group ID.
+- `expiration_timestamp` (String)
+- `project_id` (String) STACKIT Project ID to which the credential group is associated.
+
+### Read-Only
+
+- `access_key` (String)
+- `id` (String) Terraform's internal resource identifier. It is structured as "`project_id`,`credentials_group_id`,`credential_id`".
+- `name` (String)
+- `secret_access_key` (String, Sensitive)

docs/resources/objectstorage_credential.md

@@ -0,0 +1,33 @@
+---
+# generated by https://github.com/hashicorp/terraform-plugin-docs
+page_title: "stackit_objectstorage_credential Resource - stackit"
+subcategory: ""
+description: |-
+  ObjectStorage credential resource schema.
+---
+
+# stackit_objectstorage_credential (Resource)
+
+ObjectStorage credential resource schema.
+
+
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `project_id` (String) STACKIT Project ID to which the credential group is associated.
+
+### Optional
+
+- `expiration_timestamp` (String)
+
+### Read-Only
+
+- `access_key` (String)
+- `credential_id` (String) The credential ID.
+- `credentials_group_id` (String) The credential group ID.
+- `id` (String) Terraform's internal resource identifier. It is structured as "`project_id`,`credentials_group_id`,`credential_id`".
+- `name` (String)
+- `secret_access_key` (String, Sensitive)