Value from bsl.config["credentialsFile"] are not picked up at all. Rather, it's using hard coded value from our pluginspecificfields.

CI currently hardcodes credentialsFile making it inconfigurable for registry secret tests. It also mean the registry may not necessarily be using the same secret that Velero would be using during backup.
Example, setting in dpa config["credentialsFile"]="something-else/key" didnt't result in that secret which has specific changes I was testing to be used for registry pod.

This change is driven by the need to test https://issues.redhat.com//browse/OADP-463

I would also think a customer may want to similarly specify this value like how we are doing it now in a format similar to our current CI.
credentialsFile is a valid option to configure BackupStorageLocation
code

	if _, ok := bslSpec.Config["credentialsFile"]; ok { // <--Notice it ignored (_) value set here
		secretName = credentials.PluginSpecificFields[plugin].BslSecretName
		secretKey = credentials.PluginSpecificFields[plugin].PluginSecretKey
	}

Verification Steps:
specify secret name and key in DPA like this
DPA.backupLocations[].velero.config["credentialsFile"]: "<secretName>/<secretKey>"

Example spec:

spec: 
  backupLocations: 
    - velero: 
        config: 
          credentialsFile: bsl-cloud-credentials-aws-with-carriage-return/cloud
          profile: default
          region: us-east-1
        default: true
        objectStorage: 
          bucket: bucketName
          prefix: prefixName
        provider: aws
  configuration: 
    restic: 
      enable: true
      podConfig: 
        resourceAllocations: {}
    velero: 
      defaultPlugins: 
        - openshift
        - aws
        - kubevirt
      podConfig: 
        resourceAllocations: {}
  podDnsConfig: {}

OADP operator log should contain specified bucket name. For the example above, operator log should contain "got provider secret name: bsl-cloud-credentials-aws-with-carriage-return" using above spec.