feat(front): Make cluster element customizable

[maidi29]

Add possibility to edit the styling defaults of the cluster element (the number defining the count of merged markers)

Description

Currently it is not possible to adjust the styling of the cluster element. This PR adds a property clusterElementStyles where you can pass partial styling values to overwrite the default styling.

Additional context

Usage:

markerComponent.clusterElementStyles = {
  transition: "all 0.3s ease-in-out",
  hoverBackgroundColor: "#FF5733",
};

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following:

• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Follow the Conventional Commits v1.0.0 standard for PR naming (e.g. feat(examples): add hello-world example).
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.