Add Schemas as a submodule of www.openmicroscopy.org

[sbesson]

Replaces #286 but with the same goal i.e. re-include the published OME schemas under www.openmicroscopy.org/Schemas/ as part of the static Jekyll website.

As opposed to #286, most of the logic has been migrated to a submodule which is included in this repository (like #403).

Summarizing the main features:

• ome/schemas@3cfad44 extracts the history of the publish script used for generating the www.openmicroscopy.org/Schemas pages
• ome/schemas@b93e63d adds some Maven infrastructure for consuming org.openmicroscopy:specification and building the HTML pages
• ome/schemas@320f455 adds a GitHub action to generate the /Schemas page and auto-push the changes on push to master - see ome/schemas@151dac3 for an example
• https://github.com/ome/schemas/blob/master/.github/dependabot.yml configures GitHub dependabot to open PRs on new releases of the specification/plugins - see Bump specification from 5.3.0 to 6.2.1 schemas#1 followed byhttps://github.com/ome/schemas/commit/fdc888ead257b1a8dad0017075fb2e37426fc2d4 for an example of how this logic should keep the Schemas in sync with the released artifact

[sbesson]

From the HEAD of this branch, building locally gives me

[joshmoore]

This certainly matches my expectations from #403 but is even simpler. As mentioned elsewhere, I can see doing something more advanced for future versions (e.g. schemas.openmicroscopy.org) but this information will need to remain available at /Schemas permanently. This seems like a good way of doing it. 👍

[sbesson]

Now staged at https://snoopycrimecop.github.io/www.openmicroscopy.org/Schemas/ for review