Offer OSS Index user/pw for Maven

[marcelstoer]

Is your feature request related to a problem? Please describe.
Related to #4533.
The CLI and Gradle clients offer to set OSS Index user/pw. For the Maven client only the indirection through server ID and settings.xml is currently supported.

Describe the solution you'd like
For Maven, allow to either set user/pw or server ID.

I is obvious that using the server ID is usually a safer setup. However, this assumes you have access to or control over the settings.xml. This is not always the case. Example: corporate CI infrastructure with Maven settings controlled by IT.

You can still include the OSS Index for ODC safely in your pipeline if you do something like mvn -U org.owasp:dependency-check-maven:$ODC_VERSION:aggregate -DossIndexUser=$OSS_INDEX_USER ... . The actual value for $OSS_INDEX_USER would be stored as CI env variable with your project (e.g. in GitLab).

Describe alternatives you've considered
If the settings.xml isn't read-only, the pipeline might try to alter it prior to running ODC.

Additional context
@jeremylong voiced potential "endorsement" for this feature here #4533 (comment)