Move issue templates to .github folder to become community health files

[tlfeng]

Description

Currently the issue templates are put in the root directory, but not in .github directory.
The PR corrects the location for the issue templates, so that they can be a organization-wide templates.

• Move issue templates to .github folder to make them become community health files

According to the guide to create community health files:

Issue templates and their configuration file must be in a folder called .github/ISSUE_TEMPLATE.

I think with the templates put in the correct folder, the other repositories in the organization that want to use the unified issue template don't need to hold a copy of the templates in their repositories.

Testing:
I created a temporarily GitHub organization, the repository there uses the issue template (https://github.com/test-template-across-repo/repo-1/issues/new/choose) that stores in the .github repository (https://github.com/test-template-across-repo/.github/tree/main/.github/ISSUE_TEMPLATE).
[Note: I deleted the temporarily organization after 1 months.]

Issues Resolved

#9
The PR can't completely resolve the issue, we also have to remove the issue templates in the repositories that want to apply the templates here.

Check List

• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[dblock]

Oh duh this is pretty simple. Thanks!