uploadContentHandler Handle doesn't use load.FieldDelimiter for CSV loading

[juguerre]

What happened?

When bigquery python library is used for load job definition like:

job_config = bigquery.LoadJobConfig(
        source_format=bigquery.SourceFormat.CSV, schema=table.schema,
        field_delimiter=";", max_bad_records=0, skip_leading_rows=0, allow_jagged_rows=True
    )

load_job = bigquery_client.load_table_from_uri( ...

field_delimiter parameter is loaded but is never used in the emulator server. So the server is always expecting comma as field delimiter ignoring this configuration parameter.
In this situation is not possible to load CSV with delimiters different than ',' (comma).

What did you expect to happen?

Supporting single string characters for FieldDelimiter parameter is expected.

How can we reproduce it (as minimally and precisely as possible)?

Try to use bigquery_client.load_table_from_uri with a CSV file delimiter different that ','.

Anything else we need to know?

I have a little code change that fixes the issue and I can do a PR if needed/wanted.