Allow deploy without credentilas

[josephjclark]

Simple ideas for syncing credentials

openfn deploy --strip-creds --map-creds

• --strip-creds will remove all credentials before deploying
• --strip-creds a,b,c will just remove credentials a, b and c
• -- map creds a@x:b@y will map the name and owner of credential a@x to b@y. Maybe optional either side of the @

Also, as Frank has previously requested, drop unused creds (maybe allow --no-prune-creds to disable this)