ARROW-15844: [Release][Packaging] Use ASCII format for detached sign
ARROW-15844: [Release][Packaging] Use ASCII format for detached sign

We use .asc for extension. Generally, .asc is used for ASCII format.

Closes #12559 from kou/release-binary-asc

Authored-by: Sutou Kouhei <73218711cdd5d5c30ac66da3cc4d9d9204caf34b@clear-code.com>
Signed-off-by: Krisztián Szűcs <6bab32dc957a05a87930e779f272342e159326fa@gmail.com>

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