[MODERATION] organization blocking a user (#802)

- Resolves #476
- Follow up for: #540
- Ensure that the doer and blocked person cannot follow each other.
- Ensure that the block person cannot watch doer's repositories.
- Add unblock button to the blocked user list.
- Add blocked since information to the blocked user list.
- Add extra testing to moderation code.
- Blocked user will unwatch doer's owned repository upon blocking.
- Add flash messages to let the user know the block/unblock action was successful.
- Add "You haven't blocked any users" message.
- Add organization blocking a user.

Co-authored-by: Gusted <postmaster@gusted.xyz>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/802
(cherry picked from commit 0505a10421)
(cherry picked from commit 37b4e6ef9b)
(cherry picked from commit 217475385a)
(cherry picked from commit f2c38ce5c2)
(cherry picked from commit 1edfb68137)
(cherry picked from commit 2cbc12dc74)
(cherry picked from commit 79ff020f18)

routers/api/v1/user/follower.go

@@ -5,6 +5,7 @@
 package user
 
 import (
+	"errors"
 	"net/http"
 
 	user_model "code.gitea.io/gitea/models/user"
@@ -217,8 +218,14 @@ func Follow(ctx *context.APIContext) {
 	// responses:
 	//   "204":
 	//     "$ref": "#/responses/empty"
+	//   "403":
+	//     "$ref": "#/responses/forbidden"
 
 	if err := user_model.FollowUser(ctx, ctx.Doer.ID, ctx.ContextUser.ID); err != nil {
+		if errors.Is(err, user_model.ErrBlockedByUser) {
+			ctx.Error(http.StatusForbidden, "BlockedByUser", err)
+			return
+		}
 		ctx.Error(http.StatusInternalServerError, "FollowUser", err)
 		return
 	}