Additional fixes to GeoJSON req. classes regarding profiles

[jerstlouis]

Following discussions in JSON-FG SWG, I realized some additional clarifications and fixes are needed in the GeoJSON-related req. classes as a follow-up to the changes made to reflect #46 (comment):

• When JSON-FG is negotiated, the profiles returned need to be included in the links section, and optionally as HTTP Link: response headers
• The default profile does not necessarily need to be plain GeoJSON if this representation is not available (e.g., for the static server use case)
• We will need to register the various (4) DGGS-FG-JSON profiles with the naming authority (e.g., https://www.opengis.net/def/profile/ogc/0/jsonfg-dggs)
• We may need to change all current references to FG-JSON to JSON-FG as I realized this is the short name used in the Standard, which does not follow the order in the title, potentially including our name for this DGGS-optimized vector encoding: DGGS-JSON-FG instead of DGGS-FG-JSON? (see the PS of my comment here)