feat(batch-exports): Add Redshift to BatchExport destinations

[tomasfarias]

Problem

Users of the PostHog Redshift Export plugin need to be migrated over to PostHog batch exports to take advantage of the features provided by the new platform, and to be in line with the rest of the export destinations.

Changes

1. Abstract insert activity execution into a function
   Not necessary for this particular issue, but I got tired of copying and pasting Workflow code. I'll follow-up with a refactor to use the function in all other workflows.

2. Add a RedshiftBatchExportWorkflow
   This new Workflow simply calls the Postgres activity but with Redshift-specific parameters. Since we cannot do COPY on Redshift without breaking compatibility and extra complexity, we do not use the Postgres activity anymore, but instead run an INSERT query. We do re-use as much as we can from Postgres.

3. Add Redshift to BatchExport destinations
   Model updates to support the new destination

TODO:

4. Frontend support for Redshift
5. Testing

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

How did you test this code?

Locally ran unit tests:

❯ REDSHIFT_USER=user REDSHIFT_HOST=host REDSHIFT_PASSWORD=password DEBUG=1 pytest posthog/temporal/tests/batch_exports/test_redshift_batch_export_workflow.py -vv
==================================== test session starts =====================================
platform darwin -- Python 3.10.11, pytest-7.4.0, pluggy-0.13.1 -- src/github.com/PostHog/posthog/.direnv/python-3.10.11/bin/python
cachedir: .pytest_cache
django: settings: posthog.settings (from ini)
rootdir: src/github.com/PostHog/posthog
configfile: pytest.ini
plugins: icdiff-0.6, split-0.8.1, flaky-3.7.0, cov-4.1.0, asyncio-0.21.1, mock-3.11.1, Faker-17.5.0, syrupy-1.7.4, django-4.5.2, env-0.8.2
asyncio: mode=strict
collected 3 items                                                                            

posthog/temporal/tests/batch_exports/test_redshift_batch_export_workflow.py::test_insert_into_redshift_activity_inserts_data_into_redshift_table PASSED [ 33%]
posthog/temporal/tests/batch_exports/test_redshift_batch_export_workflow.py::test_redshift_export_workflow[hour] PASSED [ 66%]
posthog/temporal/tests/batch_exports/test_redshift_batch_export_workflow.py::test_redshift_export_workflow[day] PASSED [100%]

---------------------------------- snapshot report summary -----------------------------------

===================================== 3 passed in 51.14s =====================================

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