Add support for event pattern matching

[jandudulski]

Pattern matching is available in Ruby since 2.7, so the lowest supported version (it was experimental then but nothing changed in usage).

This would allow to enhance event handlers with pattern matching like:

def call(event)
  case event
  in Foo(event_id:, data: {abc: 1})
    handle_foo_for_abc_1(event_id, event)
  in Foo(data: {abc:})
    handle_foo_abc(abc)
  end # raise NoMatchingPatternError when nothing matches
end

[mostlyobvious]

Matches https://railseventstore.org/docs/contributing/maintenance_policy#ruby-versions