Extend connector download to support maven artifacts directly.

[planetf1]

The operator now supports download of additional connectors via a url/filename pair under 'Libraries' in the CR.

             libraries:
                description: Extra Libraries to be added to classpath. These are downloaded
                  during initialization. For more security use a custom container
                  image with these already present.
                items:
                  description: AdditionalDownloads - to define extra files to be downloaded
                  properties:
                    filename:
                      type: string
                    url:
                      type: string
                  type: object
                maxItems: 253
                minItems: 1
                type: array

This could be extended to support the retrieval of maven artifacts directly.

Whilst files are useful, and flexible, we do provide all of our egeria connectors as maen artifacts, and being able to simply specify a version & maven coordinate could make specification easier than composing an obscure URL

Usability improvement...

[planetf1]

We are seeing intermittent failures to retrieve artifacts from maven repositories via the sonatype nexus repo.
This impacts retrieval of our 'official' connector builds.
For example cts tests are currently failing, see odpi/egeria-test-cts#7

Either adding support for maven artifact download, or perhaps more generally, execution of a user script to retrieve additional connectors, is likely needed.