Add load node line magic documentation

[AhdraMeraliQB]

Description

Addresses #2011
Also addresses #2777

This page of the docs required several levels of changes, which have been addressed in this PR:

• Document how users can debug Kedro inside notebooks using the %load_node magic #2011 @AhdraMeraliQB & @lrcouto
• Improve documentation about %load_ext kedro.ipython to make it more visible #2777 @ankatiyar
• This comment post-#2031 - @AhdraMeraliQB

Development notes

Ignore all the early commits - this branch was created before the earlier debugging docs changes were merged into main

• Add section on %load_node line magic
• Add gif of using line magic
• Add section on debugging with the line magic
• Rejig page

Re: Rejigging the page - the following were considered:

• The flow of the page has been adapted
• Use of specific terminology (kernel, kernelspec) has been mostly removed. It has not been removed from the "Useful to know (for advanced users)" section as we expect those readers to be more advanced. The term "kernel" features in the section "Loading the project with kedro jupyter notebook" but is contextualised by the images provided, and as such I don't expect the terms to be as confusing. The following section "What does kedro jupyter notebook` do?" also makes references to the kernel established the in the section above it. Once again, as the use is contextualised, I don't expect the term to be as jarring.

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Checklist

• Read the contributing guidelines
• Signed off each commit with a Developer Certificate of Origin (DCO)
• Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• Updated the documentation to reflect the code changes
• Added a description of this change in the RELEASE.md file
• Added tests to cover my changes
• Checked if this change will affect Kedro-Viz, and if so, communicated that with the Viz team

[noklam]

Not sure if it's covered already. I think we need to mention how to find the node_name. i.e. read from the kedro's run log if it's defined already, or go to the node definition, add a node name if needed. I think this is shown in the GIF somehow but we should give clear instruction.

[AhdraMeraliQB]

The formatting on the %load_node line magic subheading was causing issues with Sphinx when referenced. Instead, I've linked to the line magic section as a whole.

[noklam]

✨thank you!

[ankatiyar]

LGTM!