New apk registry

[sobolevn]

Here are some other projects that offer apk package registries.
Required features:

• It must be free (because I cannot pay for any western services, because of the unlawful sanctions). Or it can be hosted in Russia or in any other friendly country, in this case I will be able to pay for them some reasonable price
• API access
• Public download link, something similar to what we have right now
• Security: code signing and stuff

Candidates (not full list):

• https://help.cloudsmith.io/docs/alpine-repository
• https://blog.packagecloud.io/packagecloud-a-well-suited-package-manager-for-alpine-linux

Refs:

• Use apk in release-ci #895
• release 0.5.1 for all platforms except alpine, so we can pass self-tests with the release #881
• Installation using apk package fails under Alpine  #878