fix: use background from style when creating vector tile layers

[boeckMt]

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/dlr-eoc/ukis-frontend-libraries/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)
• [x] The Project is building and passes all tests without errors

PR Type

What kind of change does this PR introduce?

• [x] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Documentation content changes
• [ ] Other... Please describe:

What is the current behavior?

On creation of vector tile layers with ol-mapbox-style, applyBackground() was not called to set the background color of the style.

What is the new behavior?

The background color is now applied to the new layer applyBackground(newlayer, style).

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

Other information

Is it part of one/more packages and which?

• @dlr-eoc/map-ol