Bump keycloak.version from 20.0.3 to 21.0.0 in /keycloak-theme (#4465)

Bumps `keycloak.version` from 20.0.3 to 21.0.0.

Updates `keycloak-server-spi` from 20.0.3 to 21.0.0
- [Release notes](https://github.com/keycloak/keycloak/releases)
- [Commits](https://github.com/keycloak/keycloak/compare/20.0.3...21.0.0)

Updates `keycloak-server-spi-private` from 20.0.3 to 21.0.0
- [Release notes](https://github.com/keycloak/keycloak/releases)
- [Commits](https://github.com/keycloak/keycloak/compare/20.0.3...21.0.0)

Updates `keycloak-services` from 20.0.3 to 21.0.0
- [Release notes](https://github.com/keycloak/keycloak/releases)
- [Commits](https://github.com/keycloak/keycloak/compare/20.0.3...21.0.0)

---
updated-dependencies:
- dependency-name: org.keycloak:keycloak-server-spi
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.keycloak:keycloak-server-spi-private
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.keycloak:keycloak-services
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

keycloak-theme/pom.xml

@@ -29,7 +29,7 @@
         <frontend.maven.plugin.version>1.12.1</frontend.maven.plugin.version>
         <frontend.maven.plugin.nodeVersion>v18.9.0</frontend.maven.plugin.nodeVersion>
 
-        <keycloak.version>20.0.3</keycloak.version>
+        <keycloak.version>21.0.0</keycloak.version>
 
         <admin-ui.path>../apps/admin-ui</admin-ui.path>
     </properties>