Add tz attribute to handlebar date function

[chroju]

Fixes #250 . Add timezone parameters to type=schedule and type=raw.

[crazy-max]

Don't think an extra timezone attribute makes sense as it should only be assigned to the date handlebar function (see my suggestion below).

[crazy-max]

Instead of an extra attribute it would be better to add an hash arg to the handlebar func like: https://handlebarsjs.com/guide/expressions.html#helpers-with-hash-arguments

date: function (format, options) {
  const m = moment(currentDate);
  Object.keys(options.hash).forEach(key => {
    switch (key) {
      case "tz":
        m.tz(options.hash[key]);
        break;
      default:
        throw new Error(`Unknown ${key} attribute`);
    }
  })
  return m.format(format);
}

# no tz
type=schedule,pattern={{date 'YYYYMMDD-hhmmss'}}
# with tz
type=schedule,pattern={{date 'YYYYMMDD-hhmmss' tz='Asia/Tokyo'}}

[chroju]

@crazy-max Thanks for your review. I have updated.

[crazy-max]

Can you also update the example in global expression section of the README: https://github.com/docker/metadata-action#date-format ?

[chroju]

Can you also update the example in global expression section of the README: https://github.com/docker/metadata-action#date-format ?

Done it !

[crazy-max]

Thanks! Can you squash your commits and update the commit message with something like:

Add tz attribute to handlebar date function

[chroju]

squashed and forced to push 👍

[crazy-max]

LGTM thanks!