Update development, troubleshooting, and process documentation

[wkurniawan07]

• Our troubleshooting guide / FAQs (https://teammates.github.io/teammates/troubleshooting-guide.html) has not been updated for very long now. Many frequent help requests should be documented, such as (but not limited to) server stuck at 85%, localhost:8080 returns 404/403, api-output is missing, front-end compilation error after pulling master branch.
• Our setup is actually compatible with Java 17 now, but we're not yet ready to make the move. Nevertheless, we should not require any devs with only Java 17 to download Java 11 exclusively for TM, but with the caveat that the officially used language is still Java 11 and thus newer language features are not to be used.
  

  teammates/docs/setting-up.md

  Line 47 in 9d0dfa4

  1. Install Java JDK 11.

• We can adopt a newer version of Contributor Covenant instead of an older version 1.4 that we are currently using.
  • Although, admittedly, this is more of a formality than anything else.
• We can add SECURITY.md to allow a more native integration for vulnerability reports.
• With GitHub Discussions becoming the main communication channel, the previous way of using issue tracker is now discontinued. All related instructions need to be updated.

There are also more parts of the documentation referring to outdated practices; those need to be updated.