Allow for custom providers hosted on maven repositories

[hwo-wd]

Extends support for custom providers ("SPIs"): while previously only http downloads were supported, the new provider definition allows for maven downloads (e.g., Apache Maven Central, Github Apache Maven (requires authn via a PAT)).

The new providers definition looks like:

keycloak_quarkus_providers:
  - id: http-client                         # required
    spi: connections                        # required if url is not specified
  - id: http-client                         # required; "{{ id }}.jar" identifies the file name on RHBK
    spi: connections                        # required if neither url, local_path nor maven are specified; required for setting properties
    default: true                           # optional, whether to set default for spi, default false
    restart: true                           # optional, whether to restart, default true
    url: https://.../.../custom_spi.jar     # optional, url for download
    url: https://.../.../custom_spi.jar     # optional, url for download via http
    local_path: my_theme_spi.jar            # optional, path on local controller for SPI to be uploaded
    maven:                                  # optional, for download using maven
      repository_url: https://maven.pkg.github.com/OWNER/REPOSITORY # optional, maven repo url
      group_id:  my.group                   # optional, maven group id
      artifact_id: artifact                 # optional, maven artifact id
      version: 24.0.4                       # optional, defaults to latest
      username:  user                       # optional, cf. https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-apache-maven-registry#authenticating-to-github-packages
      password: pat                         # optional, provide a PAT for accessing Github's Apache Maven registry
    properties:                             # optional, list of key-values

• lxml is a new python dependency for this collection (however, it was already present because it is also a dependency of middleware_automation.common

Close #222

[hwo-wd]

We now support three different kinds of providers:

• url: http download for SPIs not requiring authentication
• maven: maven download for SPIs hosted publicly on Apache Maven Central or private Maven repositories like Github Maven requiring authentication
• local_path: static SPIs to be uploaded

I think this pretty much covers the majority of use cases; future improvements might be:

• allow for authn on http (e.g. download from private Github releases), but this opens up the authn topic: basic vs. ...
• allow for latest urls on Github (since, I guess, we don't follow redirects), but having a statically fixed version is better practice anyway