SNOW-1727330, SNOW-1727332, SNOW-1727334, SNOW-1727335: Add support for DataFrameGroupBy/SeriesGroupBy.bfill/ffill

[sfc-gh-helmeleegy]

1. Which Jira issue is this PR addressing? Make sure that there is an accompanying issue to your PR.

   Fixes SNOW-1727330, SNOW-1727332, SNOW-1727334, SNOW-1727335

2. Fill out the following pre-review checklist:

   • I am adding a new automated test(s) to verify correctness of my new code
     • If this test skips Local Testing mode, I'm requesting review from @snowflakedb/local-testing
   • I am adding new logging messages
   • I am adding a new telemetry message
   • I am adding new credentials
   • I am adding a new dependency
   • If this is a new feature/behavior, I'm adding the Local Testing parity changes.
   • I acknowledge that I have ensured my changes to be thread-safe. Follow the link for more information: Thread-safe Developer Guidelines

3. Please describe how your code solves the related issue.

   Add support for DataFrameGroupBy/SeriesGroupBy.bfill/ffill.

[sfc-gh-nkrishna]

LGTM, just one comment around fixing the CHANGELOG

[sfc-gh-joshi]

LGTM, just one question: did we already support DataFrameGroupBy.fillna with both method="ffill" and method="bfill", but we just didn't expose those methods through DataFrameGroupBy.bfill and DataFrameGroupBy.ffill?

[sfc-gh-helmeleegy]

LGTM, just one question: did we already support DataFrameGroupBy.fillna with both method="ffill" and method="bfill", but we just didn't expose those methods through DataFrameGroupBy.bfill and DataFrameGroupBy.ffill?

Yes, DataFrameGroupBy.fillna was already supported.