[WIP] Adding optional field execution_state to kernel_info_reply representing shell execution status

[dby-tmwctw]

Work in progress

✨Proposing a new JEP?✨

Make sure that you have at least done the following:

1. Create a GitHub issue in the Jupyter Enhancement Proposals repo that
2. Briefly outlines the proposal
3. Suggests a review team (optional)
4. Declares why it should be a JEP (See the “JEP / Not-a-JEP Rubric” below.)
5. Identify a Shepherd to see the process through. (Shepherds are assigned
   on a round-robin basis from a set of interested engaged volunteers).
6. Decide if it's a JEP according to the criteria listed above. The Shepherd decides if the JEP criteria have been met.
7. Used the new JEP markdown template to help structure your thoughts. You can find it in jupyter-enhancement-proposal-guidelines/TEMPLATE.md in this repository.