ARROW-9308: [Format] Add Feature enum for forward compatibility.
ARROW-9308: [Format] Add Feature enum for forward compatibility.

Will start a discussion on the mailing list shortly.

Closes #7502 from emkornfield/feature_flag

Authored-by: Micah Kornfield <dbc64ab8a675880673029ed6b2cb1d084dfef0bb@gmail.com>
Signed-off-by: Micah Kornfield <dbc64ab8a675880673029ed6b2cb1d084dfef0bb@gmail.com>

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