WIP: stub sphinx example to illustrate data type relevance

[psteinb]

Description

Adding new examples to illustrate relevance of datatypes when saving and reloading images.

#4509 and #4510

Checklist

• Docstrings for all functions, psteinb: does not apply here
• Gallery example in ./doc/examples (new features only)
• Benchmark in ./benchmarks, if your changes aren't covered by an
  existing benchmark, psteinb: does not apply here
• Unit tests, psteinb: does not apply here
• Clean style in the spirit of PEP8

For reviewers

• Check that the PR title is short, concise, and will make sense 1 year
  later.
• Check that new functions are imported in corresponding __init__.py.
• Check that new features, API changes, and deprecations are mentioned in
  doc/release/release_dev.rst.
• Consider backporting the PR with @meeseeksdev backport to v0.14.x

[emmanuelle]

Hi @psteinb I will convert the status to draft so that it's clear it's not ready yet for review but it's very easy to change the status once the PR is ready.

[psteinb]

Cool, thanks. I'll see that I'll look into again in due course.