classifier used to attach the sbom should be configurable

[olamy]

currently it is hardcoded to cyclonedx. It would be nice to have it configurable something such sbom looks more appropriate.

[hboutemy]

this PR is simple, I don't have any problem with its code
my only fearing is that there is currently a naming convention that has been used to publish much content to Maven Central: is it a good idea to change?
and FYI, cyclonedx os not the only SBOM format on earth
if you really feel you are adding value to Jetty by creating your own value that nobody else uses and that hides what concrete format your project chose, tell me and I'll merge: this is simple enough

please think twice :)

[olamy]

ah you're right I forgot the story about different standards.

definitely not needed for Jetty

[hboutemy]

integrated in #506