UHF-10102: Fixes for nginx elasticsearch proxy.

[juho-lehmonen]

UHF-10102

What was done

Adds support for nginx elastic proxy in search apps.

How to test

• Detailed testing instructions in instance repositories:
  • Rekry: UHF-10102: Change local ELASTIC_PROXY_URL variable to use nginx proxy drupal-helfi-rekry#499
  • KASKO: UHF-10102: Update environment variable to use nginx elastic proxy URL. drupal-helfi-kasvatus-koulutus#652
  • KYMP: UHF-10102: Fixes for nginx elasticsearch proxy. #1007
  • SOTE: UHF-10102: Update ELASTIC_PROXY_URL variable to point to nginx proxy. drupal-helfi-sote#851
• Check that code follows our standards

Continuous documentation

• This feature has been documented/the documentation has been updated

[github-actions]

⚠️ Visual regression found! Please check if this change is wanted or accidental. You can check the output here: https://city-of-helsinki.github.io/drupal-hdbt/pull/1007/html_report/