Add flatgeobuf media type

[pjhartzell]

Related Issue(s):
#763

Description:
Adds a media type for flatgeobuf data.

PR Checklist:

• Code is formatted (run pre-commit run --all-files)
• Tests pass (run scripts/test)
• Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[codecov-commenter]

Codecov Report

Base: 94.37% // Head: 94.37% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (6e1424d) compared to base (1bdd09b).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #938   +/-   ##
=======================================
  Coverage   94.37%   94.37%           
=======================================
  Files          83       83           
  Lines       12015    12016    +1     
  Branches     1136     1136           
=======================================
+ Hits        11339    11340    +1     
  Misses        496      496           
  Partials      180      180           

Impacted Files	Coverage Δ
pystac/media_type.py	100.00% <100.00%> (ø)

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[gadomski]

Per flatgeobuf/flatgeobuf#112 (comment), it seems like there's still an open question of the "correct" media type -- @m-mohr's suggestion in that comment is application/vnd.flatgeobuf, but this PR uses application/flatgeobuf. I'm hesitant to approve w/o input form @m-mohr or someone else who might have guidance on the best one to pick for PySTAC.

[m-mohr]

I think this must be approved by the official maintainer of flatgeobuf, all other attempts from "unofficial" side just leads to issues later on, like with GeoTiff/COG where the whole community uses what we invented for STAC, but in the end we figured out that this can't be the official media type from OGC (or IANA).

[gadomski]

I've asked for guidance from the flatgeobuf folks at flatgeobuf/flatgeobuf#112 (reply in thread). Marking this PR as a draft until that question is settled.

[gadomski]

@pjhartzell per flatgeobuf/flatgeobuf#112 (reply in thread), can you update to application/vnd.flatgeobuf, and add a comment linking to that discussion?

[pjhartzell]

@gadomski Updated.

[pjhartzell]

Are we good with the enum name FGB? It was either that or FLATGEOBUF.

[gadomski]

flatgeobuf/flatgeobuf#112 (reply in thread) feels like Good Enough™ to me -- marking this as ready to review.

[pjhartzell]

@gadomski Discussion link now in comment and changelog. 🙂