refactor: update discord links to use new vanity url

.github/ISSUE_TEMPLATE/config.yml

@@ -1,7 +1,7 @@
 blank_issues_enabled: false
 contact_links:
   - name: Support via Discord
-    url: https://discord.gg/PkCWJSeCk7
+    url: https://discord.gg/overseerr
     about: Chat with users and devs on support and setup related topics.
   - name: Support via GitHub Discussions
     url: https://github.com/sct/overseerr/discussions

.github/workflows/support.yml

@@ -18,7 +18,7 @@ jobs:
             to be a support request. Please use our support channels
             to get help with Overseerr.
 
-            - [Discord](https://discord.gg/PkCWJSeCk7)
+            - [Discord](https://discord.gg/overseerr)
 
             - [GitHub Discussions](https://github.com/sct/overseerr/discussions)
           close-issue: true