Show alternative versions in the CookBook

Summary

Add a version selection menu in the CookBook. See what it looks like here: https://vpoughon.github.io/otb_cookbook_examples/.

Rationale

OTB release are not very frequent, so it's useful to be able to check the latest version of the documentation (develop), or a past version.

Implementation Details

This implementation fetches the develop version of the html div for all versions. This allows any version to show links to versions released later without rebuilding.

The file Documentation/Cookbook/_static/html/versions.html contains the list of links and needs to be kept up to date manually. Once this is merged I will add this step to the how to release wiki:

#### Update version list in CookBook

In the develop branch, update the file `Documentation/Cookbook/_static/html/versions.html` with the new version and link.

In the future it would be nice to also have a warning displayed at the top when viewing an older version of the doc, like for example the sphinxcontrib-versioning doc does that.

Copyright

The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.

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Check before merging:

• All discussions are resolved
• At least 2 votes from core developers, no vote.
• The feature branch is (reasonably) up-to-date with the base branch
• Dashboard is green
• Copyright owner has signed the ORFEO ToolBox Contributor License Agreement

added documentation label

There is a hack that will allow to show the new widget in older versions of the CookBook without rebuilding them (at least in the index page):

After this MR is merged, edit index.html and add this line before the closing </body> tag:

<script type="text/javascript" src="https://www.orfeo-toolbox.org/CookBook-develop/_static/js/versions.js"></script>

I have no way to test this unfortunately.

Does this means that we will need to modify Documentation/Cookbook/_static/html/versions.html for every new release? If so we need to add a step in the How to release!

Yes, I mention that in the MR description. We can add it to the Update Documentation section I think?

dashboard is green

merged

mentioned in commit d9d35e57

mentioned in merge request !441 (merged)

changed milestone to %7.0.0