Build and release on arm64

[DazWorrall]

Ref: https://github.com/Shopify/core-commerce-infra/issues/136

A few changes here to support multi-arch builds + releases:

• Build the debs in the test workflow so they can be reviewed without needing a release
• Update the build scripts to support multi-arch builds
• Run the build jobs on both x86 and arm64
• Build the shasum file in a separate step, when all of the files are available

[DazWorrall]

You can see the build artifacts on the workflow summary page to check the results, e.g:

$ unzip -l debs-4624a3f9ee03fd1092b88683ad1ef4a328c5d90c.zip
Archive:  debs-4624a3f9ee03fd1092b88683ad1ef4a328c5d90c.zip
  Length      Date    Time    Name
---------  ---------- -----   ----
      472  02-09-2024 13:35   ghostferry-4624a3f9ee03fd1092b88683ad1ef4a328c5d90c.sha256sum
  6162532  02-09-2024 13:35   ghostferry-copydb_1.1.0+20240209+4624a3f_amd64.deb
  5734716  02-09-2024 13:35   ghostferry-copydb_1.1.0+20240209+4624a3f_arm64.deb
  6248788  02-09-2024 13:35   ghostferry-sharding_1.1.0+20240209+4624a3f_amd64.deb
  5824666  02-09-2024 13:35   ghostferry-sharding_1.1.0+20240209+4624a3f_arm64.deb
---------                     -------
 23971174                     5 files