Added a custom Export for academicpages.github.io

[GreLucie]

Closes #12727

This PR is to add a custom exporter for academicpages.github.io by adding the corresponding layouts.
It should also implement a way to export multiple files to this format.

The .layouts file are complete but the AcademicPagesExporter class is not complete since for now, when multiple files are exported at once, they appear in the same markdown file.
We are still working on this issue and cleaning our files for a more definitive wokring PR in the future.
Complete tests also have yet to be implemented.

Steps to test

When jabref is running, go to file->Export->Export selected entries and choose "Academic Pages Markdowns" for the export type.

You can then add the markdown file to your academic page to see it on your own page.

This is just a draft pull request and it is nowhere close to being finished.

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• I manually tested my changes in running JabRef (always required)
• I added JUnit tests for changes (if applicable)
• I added screenshots in the PR description (if change is visible to the user)
• I described the change in CHANGELOG.md in a way that is understandable for the average user (if change is visible to the user)
• I checked the user documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request updating file(s) in https://github.com/JabRef/user-documentation/tree/main/en.

[github-actions]

Hey @GreLucie!

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[Siedlerchr]

You could simply switch this to a normal for loop with for (int i =1; i< entiries.length; i++) so you don't need the iterator variable.

[Siedlerchr]

Please follow the pattern of other tests in that directory, do a full comparison. of the content

[Siedlerchr]

Please revert this change

[Siedlerchr]

Use jspecify nonnull

[Siedlerchr]

is this some automatic tool that always changes the date?

[GreLucie]

Hello, you told me to revert this change so I went back to the unmodified CHANGELOG for now. I know we have to change it eventually but while this PR is just a draft we decided to change it once all the issues have been fixed.

[sadok-lajmi]

Hi, we just wanted to clarify the mechanism that we chose to implement for this new AcademicPagesExporter so that we can have your opinion on it and know whether or not it meets your expectations :
This exporter actually creates a folder at first (even when there's only one entry selected) with the name typed by the user in the export dialog and then exports all the entries selected one by one inside this folder, giving them names that match exactly what is defined by the academicpages layout as their file names in the permalink field of the markdown (that way it facilitates instant integration in the personal academic pages repository).
So is this logic fine with you or is there something we need to change especially about the creation of a folder... ?

[Siedlerchr]

Yep that sound reasonable. Go ahead