Use Fixed versioning policy

[ccremer]

⚠️
This PR changes the versioning strategy to "fixed".
Instead of publishing each package independently with each their own versioning scheme and changelog, all packages now share the same version number.
This simplifies the versioning workflow and the usage for developers. Devs don't need to check or verify whether one package is compatible with another package (e.g. whether angular package is working with core).
At the flipside, if there are breaking changes in a package that is not used, it will result in a major version update for unused packages also.

All packages will be bumped to the same version 2.0.0 to start with this versioning and indicate breaking change.

Other changes:

• Upgrades Lerna to v7
• Updates GH actions to use lerna publishing command.

Checklist for PR Authors

• Skip release if no PR matches
• Link this PR to related issues if applicable
• This PR contains a single logical change (to build a better changelog)
• I have cleaned up the commit history (no useless army of tiny "Update file xyz" commits)
• PR title doesn't contain a categorization prefix like "[chore]" or "feat:" -> There are labels for that

Checklist for PR Reviewers

• Categorize the PR by setting a good title and adding one of the release labels (see below)

  Labels that control the release

  • major: major
  • minor: minor
  • patch: patch
  • performance: patch
  • skip-release: none
  • release: Release after merge. Use together with a Label that doesn't immediately release, e.g. internal.
  • internal: none
  • documentation: none
  • tests: none
  • dependencies: none