Parameterized kernel specs

[AnastasiaSliusar]

References

This work is in progress as JEP jupyter/enhancement-proposals#87.
This PR should be reviewed when the JEP has been accepted

Code changes

There are next changes in:

• Notebook extension
• Console extension

User-facing changes

1. When a user clicks on some kernel on Notebook section on Launch panel and that kernel includes custom kernel spec variables that will be used for customization then a user will see the dialog which will suggest to configure the kernel.
2. When a user has run a kernel and then they wants to change on another kernel, then the user can call another dialog window where they can select a kernel and if this kernel includes custom kernel spec variables the user will be suggested to configure that kernel.
3. When a user clicks on some kernel on Console section on Launch panel then the user will see the same dialog with suggestions to configure a kernel.
4. If a user does not select anything and then they run a kernel, and a kernel spec file includes default values then default values will be taken.
5. If a user does not select anything and then they run a kernel, and a kernel spec file does not include default values and there are kernel variables (for example, "{raw}" in the demo video) inside kernel.json file then these variables will be cleaned and a kernel will be run without them.

Demo video: https://drive.google.com/file/d/16kPyPoowsewuYkj1-3t6q6d-5G23fsQH/view?usp=sharing

How to run

• Please use this PR with next PRs together:
  Parameterized kernel specs jupyter-server/jupyter_server#1431
  Parameterized kernel specs jupyter/jupyter_client#1028

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