Allow default override for local development - PRO-995

[Sybrand]

Summary:
Allowing the druid output folder to be configured makes it easier to run druid locally.
It's also just a generally good idea to make this configurable as opposed to hard coded.

Also: removed un-used volume while editing file.

Test Plan:
Run pipeline (especially indexing + validation) locally, and specify desired folder in DATA_OUTPUT_FOLDER and DRUID_SHARED_FOLDER environment variable.

[linear]

PRO-995