[Doc] Add Flight SQL to implementation status page

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At some point, we should probably add a dedicated section for Flight SQL to https://arrow.apache.org/docs/dev/status.html

Reporter: Antoine Pitrou / @pitrou

Related issues:

• [Doc][Flight] Mention Flight SQL in implementation status (is superceded by)

_{Note: This issue was originally created as ARROW-17618. Please see the migration documentation for further details.}

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Antoine Pitrou / @pitrou:
cc @lidavidm

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David Li / @lidavidm:
Dupe of ARROW-16384?

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David Li / @lidavidm:
But thank you for the reminder, I'll try to get this this week

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Antoine Pitrou / @pitrou:
Looks like I have a bad memory :-)