fix: fod dast-scan get-config NPE when DAST Automated scan has not been configured

[kadraman]

Updated fod dast-scan get-config to catch "unconfigured" DAST Automated configuration for release and prevent NPE. For consistency with other get-config commands now returns an empty descriptor:

---
assessmentTypeId: 0
state: Not configured

This is consistent with other scan behaviour.

Updated fod dast-scan setup-xxx to catch similar HTTP 400 exceptions and display information about why and what fields are locked. Note: currently API does not correctly identify all fields that are locked but the messaging is now more consistent, e.g.:

>fcli fod dast-scan setup-api --assessment-type="DAST Automated" --frequency="Subscription" --type="Postman"  --release 188331 --file my_postman_collection.json
FcliSimpleException: Cannot update DAST Automated scan setup for release id '188331' because scan settings are locked after scans have started. Locked settings: EnvironmentFacing Internal
        at com.fortify.cli.fod.dast_scan.helper.FoDScanConfigDastAutomatedHelper.toSetupException(FoDScanConfigDastAutomatedHelper.java:76)

These behaviours should also make the commands more suitable for use in AI Agents, MCP and/or skills.