Add a flag to warn and continue sync if deletion files are not supported in the Target

In my opinion, a warning log doesn't really fix the data inconsistency issue. However, I agree that adding a flag could be a good idea in the short term. I would suggest that the flag's default behavior should be to throw an error. We should also consider phasing it out in future releases.

_Originally posted by @ashvina in https://github.com/apache/incubator-xtable/pull/634#discussion_r1953894471_

No source file, test, or entry point is named in the issue. Begin by locating the sync path that handles deletion files unsupported by the Target and reviewing existing configuration flags; done means the behavior is configurable, defaults to throwing an error, and has coverage for warning-and-continuing.

Written by the indexing model from the issue text.