Adopt latest Wagtail logo

[lb-]

Once https://github.com/wagtail/wagtail/issues/10404 is complete - review the PRs and adopt the relevant logos in the Sphinx theme.

• https://github.com/wagtail/sphinx-wagtail-theme/tree/main/sphinx_wagtail_theme/static/img
• https://github.com/wagtail/sphinx-wagtail-theme/blob/main/docs/favicon.ico

[OsafAliSayed]

@lb- should I be replacing the wagtail-logo.svg and wagtail-logo-new.svg with updated ones from core wagtail project?

[lb-]

Yep. But I'm not sure what the new one is for, maybe it's not needed.