MM-41988 Updated links to legacy domain about.mm.com (#19552)

* Updated links to legacy domain about.mm.com

* Legacy link updates

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* Reverting - only need to change en.json

* about.mm.com URL updates

* mattermost.org URL updates

* forum.mm.org URL update

* Update .github/ISSUE_TEMPLATE.md

* Update .github/ISSUE_TEMPLATE.md

* Un-deleted language files

* Update README.md

* Update tests/test-config.json

* fix some test due to url updating (#19787)

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Harrison Healey <harrisonmhealey@gmail.com>
Co-authored-by: Ibrahim Serdar Acikgoz <serdaracikgoz86@gmail.com>

config/README.md

@@ -1,3 +1,3 @@
 # config.json
 
-This is the system configuration file for your Mattermost server. Settings are specific to different editions of Mattermost. Please read the documentation before making changes: https://about.mattermost.com/default-config-docs/
+This is the system configuration file for your Mattermost server. Settings are specific to different editions of Mattermost. Please read the documentation before making changes: https://docs.mattermost.com/configure/configuration-settings.html/