Add filter, se, sld, and wfs schemas

[jisantuc]

Overview

This PR adds sld types to the opengis package. It's not important that it's merged as much as it's important to prove that it's possible for an upcoming pr in Franklin.

Checklist

• Description of PR is in an appropriate section of the CHANGELOG and grouped with similar changes if possible

Notes

Thanks @pomadchin for help solving the schema version challenge.

Apparently RasterSymbolizer isn't included in the generated types for some reason 🤔. I'm not sure where it went. It has to be in the xsd schemas somewhere though It's in the "Symbology Encoding" (se) spec

Testing Instructions

• ++ 2.12.10; opengis/publishLocal (or another scala version that you have a convenient ammonite repl for)
• start an ammonite repl with a Scala version matching the version you published locally
• import the ivy artifact you just published:

import $ivy.`com.azavea.geotrellis::geotrellis-server-opengis:3.4.0-10-b73e8fb7-SNAPSHOT`

• import opengis.sld.<TAB> and check out what's available, import opengis.se.<TAB> and check out what's available