docs: Remove forum references and use Github Discussions (#12158)

* docs: Replace forum with Github Discussions

* Remove outdated forum link from CONTRIBUTING.md

* Remove outdated forum link from misskey-js/CONTRIBUTING.md

* Remove outdated forum link from misskey-js/docs/CONTRIBUTING.en.md

---------

Co-authored-by: かっこかり <67428053+kakkokari-gtyih@users.noreply.github.com>

CONTRIBUTING.md

@@ -15,7 +15,7 @@ Before creating an issue, please check the following:
 - To avoid duplication, please search for similar issues before creating a new issue.
 - Do not use Issues to ask questions or troubleshooting.
 	- Issues should only be used to feature requests, suggestions, and bug tracking.
-	- Please ask questions or troubleshooting in ~~the [Misskey Forum](https://forum.misskey.io/)~~ [GitHub Discussions](https://github.com/misskey-dev/misskey/discussions) or [Discord](https://discord.gg/Wp8gVStHW3).
+	- Please ask questions or troubleshooting in [GitHub Discussions](https://github.com/misskey-dev/misskey/discussions) or [Discord](https://discord.gg/Wp8gVStHW3).
 
 > **Warning**
 > Do not close issues that are about to be resolved. It should remain open until a commit that actually resolves it is merged.

packages/misskey-js/CONTRIBUTING.md

@@ -15,7 +15,7 @@ Issueを作成する前に、以下をご確認ください:
 - 重複を防ぐため、既に同様の内容のIssueが作成されていないか検索してから新しいIssueを作ってください。
 - Issueを質問に使わないでください。
 	- Issueは、要望、提案、問題の報告にのみ使用してください。
-	- 質問は、[Misskey Forum](https://forum.misskey.io/)や[Discord](https://discord.gg/Wp8gVStHW3)でお願いします。
+	- 質問は、[GitHub Discussions](https://github.com/misskey-dev/misskey/discussions)や[Discord](https://discord.gg/Wp8gVStHW3)でお願いします。
 
 ## PRの作成
 PRを作成する前に、以下をご確認ください:

packages/misskey-js/docs/CONTRIBUTING.en.md

@@ -11,7 +11,7 @@ Before creating an issue, please check the following:
 - To avoid duplication, please search for similar issues before creating a new issue.
 - Do not use Issues as a question.
 	- Issues should only be used to feature requests, suggestions, and report problems.
-	- Please ask questions in the [Misskey Forum](https://forum.misskey.io/) or [Discord](https://discord.gg/Wp8gVStHW3).
+	- Please ask questions in [GitHub Discussions](https://github.com/misskey-dev/misskey/discussions) or [Discord](https://discord.gg/Wp8gVStHW3).
 
 ## Creating a PR
 Thank you for your PR! Before creating a PR, please check the following: