Request: Support config files or env variables for easy recall

[jmdodge]

Hi - first off, great work and this is a really nice package!

I was thinking a nice feature would be to the ability to specify a configuration file or environment variables with your inputs and outputs to simplify repeated usages of the CLI commands from and to the same places.

For example, instead of

$ dbcp \
  --inputType mysql \
  --host localhost \
  --dbname mydb \
  --port 8083 \
  --user root \
  --password wp \
  --table foobar \
  --format jsonl \
  --outputFile s3://bucket/object.jsonl.gz

I might just use:

$ dbcp --config settings.json

Also useful might be declaring parameters as environment variables, like DBCP_INPUT_TYPE=mysql, DBCP_HOST=localhost, etc.
This could be especially handy for automating imports to Docker containers, etc.

Tokenizing output to allow a dynamic timestamp in the file output might also be nice, like --outputFile [long-date].sql

I know there are ways of accomplishing all of these ideas without building them into the actual package, but I thought it might be a nice suggestion.

Thanks!