adding appName alias for Session.builder.app_name

[sfc-gh-mrojas]

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 SNOW-1292271: Add required alias for appName #1348

2. Fill out the following pre-review checklist:

   • 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.

This just adds an alias such that appName will be the same as app_name

[sfc-gh-stan]

Please fix the end of file in session.py and add an entry in changelog like Exposed SessionBuilder.appName as an alias for SessionBuilder.app_name.

[sfc-gh-aalam]

Please also update session.rst so that documentation is also updated

[sfc-gh-mrojas]

@sfc-gh-aalam is this ready to merge? or there is something else missing