Replace Grunt and Browserify with Webpack to build the Webapps

[ThorbenLindhauer]

This issue was imported from JIRA:

Field	Value
JIRA Link	CAM-14613
Reporter	@tasso94
Has restricted visibility comments	false

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Motivation

While Grunt and Browserify are still actively maintained, they rarely receive software updates. There is a risk that the libraries will reach EOL at one point in the future which might block us from developing the product further. The configuration of Grunt and Browserify is rather complex leading to many configuration files scattered around the codebase. Webpack 5 is actively maintained and unlike Grunt and Browserify, not everything needs to be configured from scratch which leads to a very minimal and easy-to-read configuration. With Webpack 5 we would be well prepared for the next years to come.

Acceptance Criteria (Required on creation):

Grunt and Browserify are replaced with Webpack to build the Webapps.

Hints (optional):

Tassilo did slack time on this with the following outcome:

• Migrated the CE Webapps to Webpack (proof of concept).
• The configuration file is quite straight forward and easy-to-read.
• Grunt needs 2 minutes to build the Webapps whereas Webpack only needs 20 seconds.
• Prototype: https://github.com/camunda/camunda-bpm-platform/pull/1916

Breakdown:

### Tasks
- [x] [CAM-14657: Apply styles of Tasklist, Welcome](https://jira.camunda.com/browse/CAM-14657)
- [x] [CAM-14660: Multi-engine support doesn't work in development mode](https://jira.camunda.com/browse/CAM-14660)
- [x] [CAM-14663: Add favicon](https://jira.camunda.com/browse/CAM-14663)
- [x] [CAM-14664: Add user-styles.css](https://jira.camunda.com/browse/CAM-14664)
- [x] [CAM-14665: Integrate the webpack build into the maven reactor ](https://jira.camunda.com/browse/CAM-14665)
- [x] [CAM-14668: JQuery instead of JQLite is used by angular](https://jira.camunda.com/browse/CAM-14668)
- [x] https://github.com/camunda/camunda-bpm-platform/issues/2737
- [x] https://github.com/camunda/camunda-bpm-platform/issues/2735
- [x] https://github.com/camunda/camunda-bpm-platform/issues/2745
- [x] `*.LICENSE.txt` files are complete
- [x] https://github.com/camunda/camunda-bpm-platform/issues/2736
- [x] https://github.com/camunda/camunda-bpm-platform/issues/2744
- [x] https://github.com/camunda/camunda-bpm-platform/issues/2741
- [x] https://github.com/camunda/camunda-bpm-platform/issues/2992
- [x] https://github.com/camunda/camunda-bpm-platform/issues/2822
- [ ] #3373
- [ ] https://github.com/camunda/camunda-bpm-platform/issues/3250

Links:

[tasso94]

Dev2QA Handover

• Ensure CE and EE Webapps work as before
• Check especially the UI that is not covered by automated tests
• Ensure config.js configuration works as before for Welcome, Tasklist, Admin, and Cockpit Webapps
• Ensure plugin registration (via backend and frontend plugins) works for Welcome, Tasklist, Admin, and Cockpit Webapps

[gbetances089]

Tested along 7.20.0-alpha1 and master branch.

Test cases created based on the dev2qa comment to cover this on the next minor release, but overall looks to be ok, will keep up testing and reviewing, specially on the next patch release, but for now think we can close this.