NIFI-8526: Fix archetype

[nielsbasjes]

Thank you for submitting a contribution to Apache NiFi.

Please provide a short description of the PR here:

Description of PR

The maven archetype for creating a new processor and service essentially only work for standalone projects.
This is caused by the generated code to have the apache pom as the parent and all generated files have a license header that indicates ownership by the ASF (which in general is not true).
This makes creating a Nifi processor as a separate module in an existing project is needlessly hard.

This pull request tries to fix that.

The changes:

• I found the existing files to be uncleanly formatted so I added a .editorconfig file to aid in making them consistently formatted.
• I removed all the ASF license headers from the files that are generated.
• I added a basic "BOM" for projects to depend on. This is a basic version that will probably need additional attention. I'm not quite sure which dependencies should be mentioned in there.
• The generated projects no longer have Nifi as their parent project but now import the versions as a dependencyManagement.

I have kept these changes in separate commits in case you choose to reject for example the .editorconfig addition.

Fixes NIFI-8526.

In order to streamline the review of the contribution we ask you
to ensure the following steps have been taken:

For all changes:

• Is there a JIRA ticket associated with this PR? Is it referenced
  in the commit message?

• Does your PR title start with NIFI-XXXX where XXXX is the JIRA number you are trying to resolve? Pay particular attention to the hyphen "-" character.

• Has your PR been rebased against the latest commit within the target branch (typically main)?

• Is your initial contribution a single, squashed commit? Additional commits in response to PR reviewer feedback should be made on this branch and pushed to allow change tracking. Do not squash or use --force when pushing to allow for clean monitoring of changes.

For code changes:

• Have you ensured that the full suite of tests is executed via mvn -Pcontrib-check clean install at the root nifi folder?
• Have you written or updated unit tests to verify your changes?
• Have you verified that the full build is successful on JDK 8?
• Have you verified that the full build is successful on JDK 11?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE file, including the main LICENSE file under nifi-assembly?
• If applicable, have you updated the NOTICE file, including the main NOTICE file found under nifi-assembly?
• If adding new Properties, have you added .displayName in addition to .name (programmatic access) for each of the new properties?

For documentation related changes:

• Have you ensured that format looks appropriate for the output in which it is rendered?

Note:

Please ensure that once the PR is submitted, you check GitHub Actions CI for build issues and submit an update to your PR as soon as possible.

[github-actions]

We're marking this PR as stale due to lack of updates in the past few months. If after another couple of weeks the stale label has not been removed this PR will be closed. This stale marker and eventual auto close does not indicate a judgement of the PR just lack of reviewer bandwidth and helps us keep the PR queue more manageable. If you would like this PR re-opened you can do so and a committer can remove the stale tag. Or you can open a new PR. Try to help review other PRs to increase PR review bandwidth which in turn helps yours.