UHF-9563: add multiselect for job search area filter

[j-mys]

UHF-9563

Allow multiple areas on area filtering

What was done

• Refactored postal code UI and query logic

How to install

• Make sure your KASKO 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-9563_area_filter_multiselect
• Run make drush-cr

How to test

Go to https://helfi-rekry.docker.so/fi/avoimet-tyopaikat/etsi-avoimia-tyopaikkoja

• Select different areas, their combinations and removal with buttons
• Try refreshing page mid clicking to see if the parameters get loaded from URL.
• Check that code follows our standards

Designers review

• This PR does not need designers review

Other PRs

• The PR that this one is related to (changing the made logic)
  UHF-5253: Job search location filter #864