#12207: Fix - ScaleBox plugin - Custom scales not reported on map load

[dsuren1]

Description

This PR fixes an issue where custom scales are not correctly loaded into the ScaleBox plugin

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/geosolutions-it/MapStore2/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x", remove the others)

• Bugfix

Issue

What is the current behavior?

• ScaleBox plugin - Custom scales are not reported when opening the map #12207

What is the new behavior?
Custom scales when configured in new.json via mapOptions.view.scales now correctly loads in Scalebox

Breaking change

Does this PR introduce a breaking change? (check one with "x", remove the other)

• Yes, and I documented them in migration notes
• No

Other useful information