Validate connector config/properties for tables

To avoid confusion and "stupid" miss config it would be practical with an error message if you try to add an no valid/real attribute to the `connectors` section in table properties.

I made a mistake by putting the `append_only` attribute under `connectors` and not at top-level. I got no error message and program run fine, but of course the table was not append only. I then discovered that you can put arbitrary attribute under connectors without any errors, e.g `abc`.

Maybe add an check that attributes under connectors is an allowed/real one? I see that there is value validation for valid attributes, for example `mode` for delta input connector have value validation, checking that is is "snapshot", "follow", "snapshot_follow" or "cdc".

The following example vil run without any errors and problems. But table will not be an append only table.
```
CREATE TABLE my_table (
...
) WITH (
'connectors' = '[{
"abc"= "123",
'append_only': 'true'
...
}]'
)
```