feat(ingest): Add option to change name of database for postgres

[aseembansal-gogo]

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• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
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[hsheth2]

LGTM

In the future, we'll probably want a more principled/general way of handling this sort of modification, and ideally would have transformers to handle this. As such, I'm thinking about these changes are more of a stopgap measure.

[shirshanka]

Suggest we name the field as database_alias instead of database_identifier

[shirshanka]

LGTM!

[aseembansal-gogo]

@shirshanka I am not sure where to add the missing dependency for the test. Can you please suggest which file needs this change?

[shirshanka]

@aseembansal-gogo : this would be in setup.py

Add postgres to the base_dev_requirements variable.
near:

      *list(
         dependency
            for plugin in [
                    "bigquery",
                    "bigquery-usage",
                    "looker",
                    "glue",
                    "oracle",
                    "sagemaker",