Send omit_sections to IPython to choose which sections of documentation you don't want

[fasiha]

This PR brings to ipykernel a recent IPython PR ipython/ipython#13343 which allows us to customize IPython's responses to info and inspect messages by specifying which documentation sections we don't want. For example, numpy.sin returns the following sections:

• Call signature
• Type
• String form
• File
• Docstring
• Class docstring

and with the new omit_sections keyword argument, we can for example specify that we are not interested in the File, String form, and Type sections, thereby saving runtime and bandwidth by not generating those documentation sections.

In this present PR, we enable ipykernel's inspect message to take advantage of omit_sections. If the client provides omit_sections in its request, we'll pass it on to IPython.

Nota bene if merged, this PR should be released with an ipykernel that depends on IPython 8.0, the milestone @Carreau has set in ipython/ipython#13343.

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To test this using JupyterLab for example:

1. install ipython master
2. install this PR's branch of ipykernel (https://github.com/fasiha/ipykernel/tree/blocklist-for-inspector)
3. install https://github.com/fasiha/jupyterlab/tree/use-omit_sections branch of jupyterlab and start it: this branch has configured its inspector to omit all sections except docstrings
4. run the following in a notebook cell:

import numpy
numpy.sin
numpy.exp

5. open JupyterLab's contextual help menu and click on "exp" and "sin", etc.

Original ipykernel:

This PR with customized JupyterLab to omit numerous sections:

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Recommended triage: enhancement?

[blink1073]

Thanks again @fasiha!