add builds for arm64

[sebastianwebber]

This PR adds support for arm builds.

[lesovsky]

Hi, thank you for PR, but I have some questions:

1. Have you build pgcenter on ARM arch?
2. Have you run tests and do the tests are passed?
3. Have you check all functionality provided by pgcenter on ARM?

I am asking because I am not ARM-user and I don't have ARM devices - if some problems will occur on ARM users I unable to reproduce and handle bugs. Due to this I'd disinclined to take responsibility about proper work on platforms other than x86_64, and this is why there is only amd64 arch in build configuration.

It's quite easy to add new arch, but I must be completely sure that resulting binary will work correctly.

Now, about to PR, you added arm arch to goreleaser configuration. But besides of packages, this repo also has CI pipeline (Github Actions) and provides instructions for building docker images. If you want to implement ARM, you need to add CI instructions (see .github directory) for ARM, change existing docker builds instructions and add build instructions for amd64 and arm.