Docs: Fix the way tabs are declared

Since python doesn't have a way to lock deps for a particlar project
by default, I didn't bother with it. This resulted in mkdocs updating at
some point, bringing a breaking change to how tabs are declared and
broken tabs on docs-develop.pleroma.social. I've learned my lesson
and locked deps with pipenv in pleroma/docs!5. This MR updates Pleroma
docs to use the new tab style, fortunately my editor did most of it.

Closes #2045

docs/administration/CLI_tasks/relay.md

@@ -4,30 +4,42 @@
 
 ## Follow a relay
 
-```sh tab="OTP"
-./bin/pleroma_ctl relay follow <relay_url>
-```
+=== "OTP"
 
-```sh tab="From Source"
-mix pleroma.relay follow <relay_url>
-```
+    ```sh
+    ./bin/pleroma_ctl relay follow <relay_url>
+    ```
+
+=== "From Source"
+
+    ```sh
+    mix pleroma.relay follow <relay_url>
+    ```
 
 ## Unfollow a remote relay
 
-```sh tab="OTP"
-./bin/pleroma_ctl relay unfollow <relay_url>
-```
+=== "OTP"
 
-```sh tab="From Source"
-mix pleroma.relay unfollow <relay_url>
-```
+    ```sh
+    ./bin/pleroma_ctl relay unfollow <relay_url>
+    ```
+
+=== "From Source"
+
+    ```sh
+    mix pleroma.relay unfollow <relay_url>
+    ```
 
 ## List relay subscriptions
 
-```sh tab="OTP"
-./bin/pleroma_ctl relay list
-```
+=== "OTP"
 
-```sh tab="From Source"
-mix pleroma.relay list
-```
+    ```sh
+    ./bin/pleroma_ctl relay list
+    ```
+
+=== "From Source"
+
+    ```sh
+    mix pleroma.relay list
+    ```