Provide an enriched info actuator endpoint for monitoring purposes

[Stephan-Kok]

This PR proposes an actuator endpoint (/actuator/info).

This endpoint is in line with the other actuator endpoints we that are introduced in the Openconext landscape:

• Provide an enriched info actuator endpoint for monitoring purposes OpenConext-manage#680
• Support for logging in JSON and addition of extra information fields in the info actuator OpenConext-attribute-aggregation#148

With this PR, a version file will be created during build process in /public/version.json. This file will be used by the actuator endpoint (/actuator/info) to show information regarding when the application has been build, the current version, description and will show the amount of days passed since the release was build. This information can be used by application monitoring to determine whether a new release of the application and its middleware is required.

example /version.json:

{
    "name": "openconext/engineblock",
    "description": "OpenConext SAML proxy",
    "version": "7.0.0-dev",
    "time": "2026-05-19T12:06:37.581Z"
}

example /actuator/info:

{
  "build": {
    "name": "openconext/engineblock",
    "description": "OpenConext SAML proxy",
    "version": "7.0.0-dev",
    "time": "2026-05-18T11:59:07.992Z"
  },
  "days_since_release": 1
}

I also reviewed the implementation in the openconext/monitor-bundle, which exposes https://engine.surfconext.nl/info.
As I understand it, that implementation relies on environment variables for build metadata. Those variables are not persisted as part of the packaged application artifact, whereas this approach stores the metadata in a generated file during the build process