GH-44706: [Release][Archery][Packaging] Add "so_version" variable

[kou]

Rationale for this change

SO versions must be computed from the target version instead of embedding them to dev/tasks/tasks.yaml. Because they depend on the specified version as an argument.

What changes are included in this PR?

Add so_version variable that can be used in dev/tasks/tasks.yml.

Are these changes tested?

Yes.

#44699 (comment) used this.

Are there any user-facing changes?

No.

• GitHub Issue: [Release][Archery][Packaging] Can't use dev/release/03-binary-submit.sh on main to release #44706

[github-actions]

⚠️ GitHub issue #44706 has been automatically assigned in GitHub to PR creator.

[raulcd]

LGTM. Thanks @kou !

While this is definitely useful for future releases. We could just run for the current RC the binaries from the RC branch, right?

[kou]

Right!

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit d7bc378.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 1 possible false positive for unstable benchmarks that are known to sometimes produce them.