Metrics and middy midleware

[flochaz]

As mention by @dreamorosi there is already a middy middleware for metrics: https://middy.js.org/packages/cloudwatch-metrics/.

1. Should we encapsulate it to add the specifics we do have in PT such as ColdStartMetric ?
2. Should we just use it and use standard functions to add specifics ?
3. write a new one ?

[flochaz]

Implemetn our own for ease of maintenance