Warn users for small files processing in PutIceberg

While it can be a valid use case, it is a very bad idea to send a lot of small flow files via the PutIceberg processor as it will generate a massive amount of snapshot files. The recommendation is clearly to use a MergeContent/MergeRecord processor before the PutIceberg processor to make sure we limit the amount of individual files being sent to an Iceberg table. While we can't force a user (this could be a flow analysis rule though) we should let them know very clearly that what they're doing is likely a bad idea and let them know what is the recommended way. However if the user is sure they know what they're doing, they should be able to disable the warning.

This Jira is about adding:

• a property "Warn for small flow files" set to true by default
• a property "Minimum recommended file size" set to 10MB (depending on the previous property, if set to true)

And if the warning is enabled and a processed flow file is below the limit, then log a warning with the recommendation of using a Merge processor so that a bulletin is generated and shown to the user.