Enable new submissions via web page form

~We could use [Netlify CMS](https://www.netlifycms.org/) with GitHub integration and web3.storage API's.~

New plan, greatly simplified and more capable: base on GitHub Actions, GitHub pull request forms! :rocket: :sparkles:

Using the setup of @jcfr for the Project Week website. Refs:

- https://github.com/NA-MIC/ProjectWeek/issues/new/choose
- https://github.com/NA-MIC/ProjectWeek/issues/667
- https://github.com/NA-MIC/ProjectWeek/blob/master/.github/workflows/project-page-pull-request.yml
- https://github.com/NA-MIC/ProjectWeek/pull/668

We can likely avoid the issue creation and go forward directly with a PR from the form.

Review the referenced Project Week issue form setup, .github/workflows/project-page-pull-request.yml, and pull request 668 first. Then compare that approach with this repository's submission flow and determine the GitHub Actions and pull request form entry points needed. Done means a web form can create a pull request directly with the expected submission content.

Vom Indexierungsmodell aus dem Issue-Text verfasst.