Use absolute link to CODE_OF_CONDUCT.md in issue templates

[F21]

Resolves #1456

---

Behavior

Before the change?

The link to the code of conduct in the issue templates is a relative link, so it links to https://github.com/integrations/terraform-provider-github/issues/CODE_OF_CONDUCT.md

After the change?

This PR fixes the link by using the absolute link to the file.

Other information

None

Additional info

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Added the appropriate label for the given change

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes (Please add the Type: Breaking change label)
• No

If Yes, what's the impact:

• N/A

Pull request type

Please add the corresponding label for change this PR introduces:

• Bugfix: Type: Bug
• Updates to docs or samples: Type: Documentation

---

[kfcampbell]

Ahh, thanks for fixing this! It looks like we had some automation that assumed incorrect values.