Update keycloak.yml

[dennemark]

Newest version 26.0.2
Postgres version 16

--proxy was deprecated
---proxy-headers=xforwarded is necessary
and for replacement of --proxy=edge also --http-enabled=true

ENV variables were changed, too.

https://www.keycloak.org/docs/latest/upgrading/index.html#deprecated-proxy-option

☑️ Self Check before Merge

• I have tested the template using the method described in README.md thoroughly
• I have ensured that I put as much default values as possible (except passwords) to ensure minimum effort required for end users to get started.
• I have ensured that I am not using the "latest" tag as this tag is dynamically changing and might break the one-click app. Use a fixed version.
• I have made sure that instructions.start and instructions.end are clear and self-explanatory.
• Icon is added as a png file to the logos directory.
• I've executed the checks if necessary by running npm ci && npm run validate_apps && npm run formatter (If failling run the prettier: npm run formatter-write)
• I will take responsibility addressing any issues that arises as a result of this PR (maintaining this app).

[githubsaturn]

Thanks!