Map viewer / WFS filter / remove unused SLD API endpoints

[juanluisrp]

Summary

The SLD-based WMS filtering strategies (SLD and SLD_BODY) were never
the active path in production: the default filterStrategy was always
FILTER, the SLD/SLD_BODY options were commented out in the viewer config,
and the SLD_BODY path is documented as returning 414 Request-URI Too Large.

• Remove dead endpoints POST /sld, GET /sld, DELETE /sld, GET /sld/{id}.xml, GET /sldform from SldApi, keeping only POST /filter.
• Remove SLD-only helpers from SLDUtil (parseSLD, getGetStyleRequest, insertFilter) and their associated imports (Apache HttpClient, IOUtils, javax.mail, JDOM, etc.).
• Remove TextFile JPA entity and TextFileRepository (existed solely to persist generated SLD documents); add a v4412 migration to drop the files table and sequence.
• Simplify WfsFilterService to always POST to /api/tools/ogc/filter and apply the result as a WMS FILTER parameter; remove the isSld/SLD_BODY branches, both pollSldUrl copies, and the $timeout/gnWfsFilterConfig injections.
• Remove the filterStrategy property from the gnWfsFilterConfig constant and the dead var isSld line in filterWMS in WfsFilterDirective.
• Remove stale generateSLD/getSLD Jeeves security mappings.
• Update user guide to reflect that filters are applied via the WMS FILTER parameter.

Test plan

• POST /geonetwork/srv/api/tools/ogc/filter returns HTTP 201 with a valid <ogc:Filter> XML body
• GET /sldform, GET /sld, GET /sld/1.xml, POST /sld, DELETE /sld all return HTTP 404
• wfsFilterService.pollSldUrl no longer exists on the service
• wfsFilterService.getFilter → applyFilter sets FILTER param on WMS layer source; SLD and SLD_BODY params are not set
• Tested end-to-end with real data
• No console errors in the map viewer