UHF-8787: Fix metro color palette hover text color

[teroelonen]

UHF-8787

What was done

• Changed the --hdbt-color-palette-button-contrast--secondary variable color to white since it was incorrectly black and invisible when hoverin over a button.

How to install

• Make sure your instance is up and running on latest dev branch.
  • git pull origin dev
  • make fresh
• Update the HDBT theme
  • composer require drupal/hdbt:dev-UHF-8787_metro_hover_color_fix
• Run make drush-cr

How to test

• To thoroughly test this issue you can use KASKO instance and its front page. There is already one paragraph now that has the issue visible: "Tutustu meihin työnantajana" block. Check that it works now on hover.
• Test that the same block with the button as "Full color" works as well when hovering over the button.
• Now change the paragraph to "Image on right" design and test that the both button variants work with this background color as well.
• Make sure that the banners work as well. Add banner on the page with a link using style of "Full color background" and make sure it works correctly when hovered.
• Now make a banner with a link using style of "Only borders" and make sure it works correctly on hover as well.
• Check that code follows our standards

Designers review

• This PR does not need designers review
• This PR has been visually reviewed by a designer (Name of the designer)

[Arkkimaagi]

I removed the committed js codes to keep this clean. Approved.