implement generalised PaleyII symmetric conference matrices

[dimpase]

Currently only symmetric conference matrices obtained from $GF(q)$ using Paley construction for $q\equiv 1\mod 4$
are used in building Hadamard matrices by PaleyII construction. But we can do better, use
any symmetric conference matrix known to Sage.

The 1st new to Sage example is of order 4*787

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

[github-actions]

Documentation preview for this PR (built with commit 4d56220; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[dimpase]

@MatteoCati - have you got around to look into this? If not, I can finish this myself.

[MatteoCati]

I've created a PR to add the code to this branch dimpase#7 since I could not edit the branch directly.
I (incorrectly) assumed you would have received a notification about it.

[dimpase]

Build documentation failure is a red herring, it seems.

@MatteoCati - ready for review

[dimpase]

@kwankyu - do you have an idea why CI docbuild fails here (at the place where html docs update is handled by git merge
(or maybe git stash) ? It looks like a bug in the CI.

[kwankyu]

Yes. The blocker fixes the bug in ci: #38468

You may merge the PR to build doc preview.

The blocker has been slumbering there for at least three weeks. That is why I am suggesting this: https://groups.google.com/g/sage-devel/c/ad9hQZw1PKQ

[kwankyu]

Otherwise lgtm.

[dimpase]

Thanks, I've fixed one of the things you pointed out. As to various .'s, it would need to be done consistently, through the codebase - where these vary.

[kwankyu]

I think you can set this to "positive review" since @MatteoCati implicitly acknowledged it.

[dimpase]

Thanks!