hardis:org:data:delete doesn't support full range of delete operations

[readeral]

Currently SFDMU offers the following deletion options:

• Delete
• HardDelete
• DeleteSource
• DeleteHierarchy

DeleteSource operates on the source only, but the rest all require a target org. sfdx-hardis delete command only works with deletesource as it only uses the --sourceusername flag.

Related to #786 using the 'delete' option enables cleaning up the target before uploading data from source using objectSets. Supporting the full range of options would require a refactor, I can have a look at all this eventually.

[readeral]

I've removed my two paragraphs about safety.. I see you've got plenty of checks to ensure you can't accidentally run it in production!

[nvuillam]

@readeral indeed i wanted to make sure to avoid accidents in production :)
I didn't know about the other options, plz be my guest for a PR to branch migrate-sf-plugin :)