Update .github docs

[ngie-eign]

Description

CONTRIBUTING.md

• Fix relative pathing to other .github Markdown docs.
• Update/correct request forwarding, as the Issues tracker has been disabled for the repo.

CODE_OF_CONDUCT.md

• Fix a grammar nit.
  • eg should be spelled e.g., as it's an acronym.
• Remove a broken link to the TODO group's CoC template.
  • It's been updated significantly, along with the URL. Referring to it by a direct link doesn't make sense--unless using a service like archive.org.

CONTRIBUTING.md

• Fix relative pathing to other .github Markdown docs.
• Update/correct request forwarding, as the Issues tracker has been disabled for the repo.

ISSUE_TEMPLATE.md

Remove since the Issue tracker has been disabled on the repo.

PULL_REQUEST_TEMPLATE.md

Fix branding for GitHub.