* Install Node.js 14.x on compose-full-changelog workflow

* change date formate in changelog file name

* improve node js installation in workflow

* add PR template file

* Update .github/PULL_REQUEST_TEMPLATE.md

Co-authored-by: per1234 <accounts@perglass.com>

* Update .github/PULL_REQUEST_TEMPLATE.md

Co-authored-by: per1234 <accounts@perglass.com>

Co-authored-by: per1234 <accounts@perglass.com>

The "Compose full changelog" GitHub Actions workflow generates a changelog file from the release notes and uploads this
to Arduino's server for display to the user by the IDE updater.

Previously, this workflow could be triggered by either of two events:

- Release creation
- Release edit

To reduce the possibility of endless recursion, GitHub Actions ignores events which are triggered using the
auto-generated `GITHUB_TOKEN` access token. All release creations are done automatically by the "Arduino IDE" GitHub
Actions workflow, which uses this token.

For this reason, the release creation trigger will never be used. Since the behavior of the event being ignored by
GitHub Actions under these conditions is not at all obvious, having the workflow configured for such an irrelevant
trigger can cause confusion.

The workflow will be triggered by the manual edit which is done on every release to format the raw release notes
auto-generated from the commit history. So the fact that the release creation trigger doesn't work is not a problem.

Linux x86-64 builds of the Arduino IDE are now available in AppImage format in additional to the ZIP format.

Since only the AppImage format IDE supports auto-updates (the IDE installed from the ZIP will notify of available updates, but can't auto-update), this will be the preferred format and so good beta testing coverage of it is especially important.

When using the interactive installer, the user is presented with a dialog requested they agree to this.

The previous statement about initiation of a download constituting agreement is relevant in the context of the text's source on the arduino.cc downloads page, but not at all in the context of the installer dialog.

Co-authored-by: Umberto Sgueglia <umberto.sgueglia@external.fcagroup.com>