Create a complete PR template for this repo

### What would you like to be added?

We need a complete PR template for this repo which includes all the things we want contributors to do, including:

* please search if there's already a pending PR that does the same thing
* instructions for AI
* release note requirement
* don't use "Fixes"

Plus probably other stuff; let's add requirements here. We can [start with the k/k one](https://github.com/kubernetes/kubernetes/blob/master/.github/PULL_REQUEST_TEMPLATE.md).

@ivanvc @serathius @siyuanfoundation @fuweid @ahrtr

### Why is this needed?

New contributors are making mistakes with PRs because they don't know the rules.

Start by checking the repository's existing .github pull request templates and compare them with Kubernetes' .github/PULL_REQUEST_TEMPLATE.md. Gather the contribution requirements listed in the issue, clarify the additional requirements with maintainers, and consider the work done when the agreed complete template is added and its guidance covers those requirements.

Written by the indexing model from the issue text.