chore: use single default pr template

.github/PULL_REQUEST_TEMPLATE/ci.md

@@ -1,7 +0,0 @@
-Fixes <issue-or-jira-number>
-
-## PR Checklist
-Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:
-
-- [ ] If changed package build ci, pass [this action](https://github.com/emqx/emqx/actions/workflows/build_packages.yaml) (manual trigger)
-- [ ] Change log has been added to `changes/` dir for user-facing artifacts update

.github/PULL_REQUEST_TEMPLATE/doc.md

@@ -1 +0,0 @@
-Fixes <issue-or-jira-number>

.github/PULL_REQUEST_TEMPLATE/v4.md

@@ -1,12 +0,0 @@
-Fixes <issue-or-jira-number>
-
-## PR Checklist
-Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:
-
-- [ ] Added tests for the changes
-- [ ] Changed lines covered in coverage report
-- [ ] Change log has been added to `changes/` dir
-- [ ] `appup` files updated (execute `scripts/update-appup.sh emqx`)
-- [ ] For internal contributor: there is a jira ticket to track this change
-- [ ] If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
-- [ ] In case of non-backward compatible changes, reviewer should check this item as a write-off, and add details in **Backward Compatibility** section

.github/pull_request_template.md

@@ -9,3 +9,8 @@ Please convert it to a draft if any of the following conditions are not met. Rev
 - [ ] For internal contributor: there is a jira ticket to track this change
 - [ ] If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
 - [ ] Schema changes are backward compatible
+
+## Checklist for CI (.github/workflows) changes
+
+- [ ] If changed package build workflow, pass [this action](https://github.com/emqx/emqx/actions/workflows/build_packages.yaml) (manual trigger)
+- [ ] Change log has been added to `changes/` dir for user-facing artifacts update