[Release] Add a post script to generate announce email

[asfimport]

We want to generate an announce email like a vote email.

e.g.: [ANNOUNCE] Apache Arrow 10.0.0 released
https://lists.apache.org/thread/zdsogdwj3r7wjv93o84go4ykgrcwtr0p .

FYI: We can generate a vote email by SOURCE_DEFAULT=0 SOURCE_VOTE=1 dev/release/02-source.sh ...

Reporter: Kouhei Sutou / @kou

_{Note: This issue was originally created as ARROW-18414. Please see the migration documentation for further details.}

[thisisnic]

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