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>

gitea/resource_gitea_team_membership.go

@@ -0,0 +1,111 @@
+package gitea
+
+import (
+	"fmt"
+
+	"code.gitea.io/sdk/gitea"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+)
+
+const (
+	membershipTeamID 	string = "team_id"
+	membershipUserName 	string = "username"
+)
+
+func resourceTeamMembershipCreate(d *schema.ResourceData, meta interface{}) (err error) {
+	client := meta.(*gitea.Client)
+
+	team_id := d.Get(membershipTeamID).(int)
+	username := d.Get(membershipUserName).(string)
+
+	// Create the membership
+	_ , err = client.AddTeamMember(int64(team_id), username)
+
+	// What if the membership exists? Consider error messages
+	// Does this do anything? Will err not be return in the end anyway
+	if err != nil {
+		return
+	}
+	
+	err = setTeamMembershipData(team_id, username, d)
+
+	return
+}
+
+func resourceTeamMembershipRead(d *schema.ResourceData, meta interface{}) (err error) {
+	client := meta.(*gitea.Client)
+	
+	var resp *gitea.Response
+
+	team_id := d.Get(membershipTeamID).(int)
+	username := d.Get(membershipUserName).(string)
+
+	// Attempt to get the user from the team. If the user is not a member of the team, this will return a 404 
+	_, resp, err = client.GetTeamMember(int64(team_id), username)
+	if err != nil {
+		return err
+	}
+
+	// The membership does not exist in Gitea
+	if resp.StatusCode == 404 {
+		// No ID in the resource indicates that it does not exist
+		d.SetId("")
+		return nil
+	}
+
+	err = setTeamMembershipData(team_id, username, d)
+
+	return
+}
+
+func resourceTeamMembershipDelete(d *schema.ResourceData, meta interface{}) (err error) {
+	client := meta.(*gitea.Client)
+
+	team_id := d.Get(membershipTeamID).(int)
+	username := d.Get(membershipUserName).(string)
+
+	// Delete the membership
+	_, err = client.RemoveTeamMember(int64(team_id), username)
+
+	if err != nil {
+		return err
+	}
+
+	return
+}
+
+func setTeamMembershipData(team_id int, username string, d *schema.ResourceData) (err error) {
+	// This can't be team or usename only as that would not be unique since the
+	// team can have multiple members and the user can have multiple memberships. 
+	d.SetId(fmt.Sprintf("%d_%s", team_id, username))
+	d.Set(membershipTeamID, team_id)
+	d.Set(membershipUserName, username)
+
+	return
+}
+
+func resourceGiteaTeamMembership() *schema.Resource {
+	return &schema.Resource{
+		Read:   resourceTeamMembershipRead,
+		Create: resourceTeamMembershipCreate,
+		Delete: resourceTeamMembershipDelete,
+		Importer: &schema.ResourceImporter{
+			StateContext: schema.ImportStatePassthroughContext,
+		},
+		Schema: map[string]*schema.Schema{
+			"team_id": {
+				Type:        schema.TypeInt,
+				Required:    true,
+				ForceNew:    true,
+				Description: "The ID of the team.",
+			},
+			"username": {
+				Type:        schema.TypeString,
+				Required:    true,
+				ForceNew:    true,
+				Description: "The username of the team member.",
+			},
+		},
+		Description: "`gitea_team_membership` manages a single user's membership of a single team.",
+	}
+}