New resources for managing team membership (#36)

This PR adds two new resources, _gitea_team_membership_ & _gitea_team_members_, in an attempt to decouple _gitea_team_ resources from team memberships. This facilitates the removal of members from teams without altering/recreating an existing _team_ resource.

This PR adresses this issue: https://gitea.com/gitea/terraform-provider-gitea/issues/30

The ability to set members in the _gitea_team_ resource has been removed.

The resources proposed here are inspired by similar resources in the _GitHub_ provider:
* [team_members](https://registry.terraform.io/providers/integrations/github/latest/docs/resources/team_members)
* [team_membership](https://registry.terraform.io/providers/integrations/github/latest/docs/resources/team_membership)

# gitea_team_members
A single resource manages all members of a team.

- This resource must be recreated when membership changes. This means, that other team members will temporarily loose their membership until the recreation of the resource is complete.
- If the recreation of the resource fails, other users will have lost their membership until the resource can be recreated.

# gitea_team_membership
A single resource holds the relationship between a single user and a single team.

-  Memberships can be deleted without affecting other users.

Reviewed-on: https://gitea.com/gitea/terraform-provider-gitea/pulls/36
Reviewed-by: techknowlogick <techknowlogick@noreply.gitea.com>
Co-authored-by: Tobias Balle-Petersen <tobiasbp@gmail.com>
Co-committed-by: Tobias Balle-Petersen <tobiasbp@gmail.com>

docs/resources/team.md

@@ -69,7 +69,6 @@ resource "gitea_team" "test_team_restricted" {
 - `can_create_repos` (Boolean) Flag if the Teams members should be able to create Rpositories in the Organisation
 - `description` (String) Description of the Team
 - `include_all_repositories` (Boolean) Flag if the Teams members should have access to all Repositories in the Organisation
-- `members` (List of String) List of Users that should be part of this team
 - `permission` (String) Permissions associated with this Team
 Can be `none`, `read`, `write`, `admin` or `owner`
 - `repositories` (List of String) List of Repositories that should be part of this team

docs/resources/team_members.md

@@ -0,0 +1,51 @@
+---
+# generated by https://github.com/hashicorp/terraform-plugin-docs
+page_title: "gitea_team_members Resource - terraform-provider-gitea"
+subcategory: ""
+description: |-
+  gitea_team_members manages all members of a single team. This resource will be recreated on member changes.
+---
+
+# gitea_team_members (Resource)
+
+`gitea_team_members` manages all members of a single team. This resource will be recreated on member changes.
+
+## Example Usage
+
+```terraform
+resource "gitea_org" "example_org" {
+  name = "m_example_org"
+}
+
+resource "gitea_user" "example_users" {
+  count      = 5
+  username   = "m_example_user_${count.index}"
+  login_name = "m_example_user_${count.index}"
+  password   = "Geheim1!"
+  email      = "m_example_user_${count.index}@user.dev"
+}
+
+resource "gitea_team" "example_team" {
+  name         = "m_example_team"
+  organisation = gitea_org.example_org.name
+  description  = "An example of team membership"
+  permission   = "read"
+}
+
+resource "gitea_team_members" "example_members" {
+  team_id = gitea_team.example_team.id
+  members = [for user in gitea_user.example_users : user.username]
+}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `members` (List of String) The user names of the members of the team.
+- `team_id` (Number) The ID of the team.
+
+### Read-Only
+
+- `id` (String) The ID of this resource.

docs/resources/team_membership.md

@@ -0,0 +1,52 @@
+---
+# generated by https://github.com/hashicorp/terraform-plugin-docs
+page_title: "gitea_team_membership Resource - terraform-provider-gitea"
+subcategory: ""
+description: |-
+  gitea_team_membership manages a single user's membership of a single team.
+---
+
+# gitea_team_membership (Resource)
+
+`gitea_team_membership` manages a single user's membership of a single team.
+
+## Example Usage
+
+```terraform
+resource "gitea_org" "example_org" {
+  name = "m_example_org"
+}
+
+resource "gitea_user" "example_users" {
+  count      = 5
+  username   = "m_example_user_${count.index}"
+  login_name = "m_example_user_${count.index}"
+  password   = "Geheim1!"
+  email      = "m_example_user_${count.index}@user.dev"
+}
+
+resource "gitea_team" "example_team" {
+  name         = "m_example_team"
+  organisation = gitea_org.example_org.name
+  description  = "An example team for membership testing"
+  permission   = "read"
+}
+
+resource "gitea_team_membership" "example_team_memberships" {
+  for_each = { for user in gitea_user.example_users : user.username => user }
+  team_id  = gitea_team.example_team.id
+  username = each.value["username"]
+}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `team_id` (Number) The ID of the team.
+- `username` (String) The username of the team member.
+
+### Read-Only
+
+- `id` (String) The ID of this resource.