chore: apache license eslint rule

[TannerGilbert]

Adds Eslint plugin to check if files contain license header.

Used plugin: https://github.com/Stuk/eslint-plugin-header

Removed all the Eslint files for the packages as they are currently not customizing anything. If a Eslint file is added to a package the header rule must be overridden to change the path of the file:

Example:

module.exports = require('@backstage/cli/config/eslint-factory')(__dirname, {
  overrides: [
    {
      "files": ["*.ts", "*.tsx", "*.js", "*.jsx"],
      "rules": {
        "header/header": ["error", "../../header.js"]
      }
    }
  ],
});

Known issues:

• Empty first line breaks the header plugin Stuk/eslint-plugin-header#47

[heinzburgstaller]

We should get rid of the tabs, looks weirdly formatted

There is also a short version available https://www.apache.org/foundation/license-faq.html#Apply-My-Software

Copyright [yyyy] [name of copyright owner]
SPDX-License-Identifier: Apache-2.0

[MrManny]

I would like to verify if the shortened version of the license header can be applied. I think @agrimmer or OSPO might have a better idea in this case. For now, I would prefer it to be more verbose than possibly needed - better safe than sorry :)

But yeah, if the tabs can be eliminated, that'd be great. I think (but I am not 100% sure) that template strings might be able to handle this.

[agrimmer]

I woud keep the long version as seems to be standard for other plugins. See e.g.
https://github.com/backstage/backstage/blob/master/plugins/github-issues/src/index.ts

However, can we remove the brackets in [2024] and [Dynatrace].

[MrManny]

Change requests:

• adjust pattern and template to avoid square brackets,
• if possible, the tabs in the rest of the rule could be improved as per previous comments.