Rename flight-sql-experimental to flight-sql

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
The arrow-flight crate has a feature flag named flight-sql-experimental:

arrow-rs/arrow-flight/Cargo.toml

Line 64 in 915e992

flight-sql-experimental = ["dep:arrow-arith", "dep:arrow-data", "dep:arrow-ord", "dep:arrow-row", "dep:arrow-select", "dep:arrow-string", "dep:once_cell", "dep:paste"]

However this feature has been used for several years now in several production systems. I think the experimental name is misleanding

Describe the solution you'd like

Remove the experimental from the flag name

Describe alternatives you've considered
To keep it backwards compatible, I recommend:

1. Rename flight-sql-experimental to flight-sql
2. Add a new flight-sql-experimental feature that just activates flight-sql with a comment to remove it after a while

Additional context

[kunalsinghdadhwal]

@alamb Kindly review