Update runtime

[ruslandoga]

This PR updates Erlang/Elixir/Alpine versions to the current latest.

Context: #44 (comment)

UPDATE: the container fails to start right now with

ERROR! Cannot configure :kernel because :reboot_system_after_config has been set to false and :kernel has already been loaded, meaning any further configuration won't have an effect.

The configuration for :kernel before config providers was:

nil

The configuration for :kernel after config providers was:

[inet_dist_listen_min: 30000, inet_dist_listen_max: 30000]

Runtime terminating during boot ({<<"aborting boot">>,[{'Elixir.Config.Provider',boot,2,[]}]})

Crash dump is being written to: erl_crash.dump...done

(I had to switch from config/releases.exs to config/runtime.exs to get this error message, with the former it was just erl_crash.dump)

I'll make the following changes before marking the PR ready for review:

• switch to runtime.exs
• use vm.args.eex for :kernel configuration or set reboot_system_after_config to true

[ruslandoga]

Should we also install ca-certificates (for the new public_key.cacerts_get) and ncurses (I never learned why it is needed in Erlang, but I think my apps fail to start when it's missing)?