[UWS,TAP] Fix the configuration file for the UPLOAD feature.

The property `upload_default_db_limit` has been deprecated. Indeed, in the
current state of the TAP protocol, this makes no sense: the user can not change
the limit size (in bytes or rows) for uploaded tables.

The property `upload_max_file_size` has been deprecated. It is actually
duplicated: `upload_max_db_limit`, if expressed in bytes already lets put a
limit on the maximum size of an uploaded table/file.

The property `upload_max_request_size` has been added. It lets set a maximum
size for a whole HTTP Multipart Request. By default it is set to 250MB.

The default value of `upload_max_db_size` is now 1 million rows.

The UPLOAD feature is still disabled by default (i.e. `upload_enabled=false`).