Why we create this PR?

This PR contains the following changes:

added eclipse-dash-license action and workflow
Updated license headers in workflow files
Removed GHCR references from workflows
Refactor and optimize workflows
Updated user(10001)/group(10001) ids to Dockerfiles and helm values
Moved hardcoded values from helm templates and make them configurable from helm values
Removed standalone backend helm chart from the dpp-backend directory
Updated PULL_REQUEST_TEMPLATE.md
Added enable/disable feature to the dpp-frontend helm chart

What we want to achieve with this PR?

Optimize workflows and helm charts. Removed unnecessary content/files to clean the repository

Updated license headers in workflow files
Refactor and optimize workflows
Updated user(10001)/group(10001) ids to Dockerfiles and helm values
Moved hardcoded values from helm templates and make them configurable from helm values
Updated PULL_REQUEST_TEMPLATE.md
Updated Arc42.md
Updated AdminGuide.md