Update ssh setup guide

[niksirbi]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?
See issue #61.

What does this PR do?

Closes #61 by introducing the following changes:

• Delete section on remote ssh via VSCode, because of Docs currently suggest to use VSCode in the bastion node #62
• Add a warning about doing tasks on the bastion and gateway nodes (with an example of how to use interactive jobs for quick tasks).
• Add a note about managed desktop computers (because their ssh setup is much simpler, or even unnecessary).
• Update the flowchart to distinguish between unmanaged vs managed machines.

This PR does not provide an updated "Remote development via VSCode" section, as I plan to write a new standalone how-to guide specifically on this task, based on the discussion in #62.

How to review

It's best to locally build and render the website, as the guide contains many interactive elements (from sphinx-design and myst-markdown):

git clone https://github.com/neuroinformatics-unit/HowTo.git
cd HowTo

# First time only
pip install -r docs/requirements.txt
sphinx-build docs/source docs/build

# Every time you want to update the local build
rm -rf docs/build && sphinx-build docs/source docs/build

# To view website, open docs/buid/index.html

[lauraporta]

Content looks good to me 👍 Also renders well on Chrome locally