Adds support for full threshold syntax

[mwain]

While running some tests the initializer couldn't marshal the full threshold syntax.
Threshold syntax is docs:

export const options = {
  thresholds: {
    metric_name1: ['threshold_expression', `...`], // short format
    metric_name2: [
      {
        threshold: 'threshold_expression',
        abortOnFail: true, // boolean
        delayAbortEval: '10s', // string
      },
    ], // full format
  },
};

This adds support for full and short versions of thresholds using stats.Thresholds

[CLAassistant]

All committers have signed the CLA.

[yorugac]

Hi @mwain, thank you for the contribution 🙂

Your PR seems fine to me, code-wise 👍 Next week, I'll run a few more tests and if nothing unusual comes up, will merge it in.

[yorugac]

LGTM 👍