Lock plugin versions and OTP upgrade

[albsch]

Remove support for older OTP versions, linting requires OTP 23

• Workflow uses Erlang 23 & 24
• Locked rebar3 plugins
• Formatted all files with erlfmt

[define-null]

You might want to lock plugin versions as well, that was the cause for build break. We did the following in our fork: (https://github.com/vaxine-io/vaxine/blob/5e206664346d2acfbd35f2c0e72dd1943112789f/rebar.config#L6) By the way rebar3_format is probably redundant, given that erlfmt is used at the moment.

[albsch]

rebar3_format is needed to be able to use rebar3 format without calling erlfmt directly.