SNOW-664934 Support schema for pandas DF in create_dataframe()

[sfc-gh-sfan]

Description

Prior to this change, schema is ignored if the input data is a pandas DF in create_dataframe(). This can be confusing as user would expect schema to take effect.

Note that this is a behavior change.

Testing

integ test

Please answer these questions before submitting your pull requests. Thanks!

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

   Fixes #504

2. Fill out the following pre-review checklist:

   • [x] I am adding a new automated test(s) to verify correctness of my new code
   • [ ] I am adding new logging messages
   • [ ] I am adding a new telemetry message
   • [ ] I am adding new credentials
   • [ ] I am adding a new dependency

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

   Prior to this change, schema is ignored if the input data is a pandas DF in create_dataframe(). This can be confusing as user would expect schema to take effect.

[sfc-gh-sfan]

This is a behavior change and the next scheduled behavior change release is going to be next year, so this PR will be shelved until we are ready for next BCR.