Create an init config alter hook and a new klaro submodule to set klaro specific init settings

Problem/Motivation

Currently, we are using a not so nice workaround to set the `cookieless_mode` for when klaro is installed:

  if (\Drupal::moduleHandler()->moduleExists('klaro') && !isset($initConfigJson['cookieless_mode'])) {
    $initConfigJson['cookieless_mode'] = 'on_reject';
  }

This is ok, but an alter hook, to alter the initConfigJson + a dedicated "posthog_klaro" submodule, which automatically enables the klaro "posthog" config on install (if it exists and is not already enabled) and contains a dependency on klaro in the info.yml would be nicer.

Steps to reproduce

Proposed resolution

Create an init config alter hook and a new klaro submodule to set klaro specific init settings

Remaining tasks

User interface changes

API changes

Data model changes