Release 2021.5.1

Code Health

1. Check the responses of prompts for installation of missing packages such as IPyKernel.
   (#5432)

Fixes

1. Fix for 'Export as Python Script' option not appearing.
   (#5403)
2. Delete extension context secrets if we get an error when getting them.
   Small fixes on error handling.
   (#5419)
3. Enable correct plot background for Native Notebooks.
   (#5353)
4. Stop asking users to install ipykernel on autostart, only do it when a cell is ran.
   (#5368)
5. Invalidate cached interpreters when Python extension active interpreter changes.
   (#5470)