[general] Rename issue template from md to yml

Signed-off-by: Timothy Chen <timothytim@google.com>
diff --git a/.github/ISSUE_TEMPLATE/darjeeling-issue.md b/.github/ISSUE_TEMPLATE/darjeeling-issue.yml
similarity index 100%
rename from .github/ISSUE_TEMPLATE/darjeeling-issue.md
rename to .github/ISSUE_TEMPLATE/darjeeling-issue.yml