Missing `customMetrics` from DecoratedFastify type

[danibix95]

Hi,

using custom-plugin-lib with Typescript I noticed that DecoratedFastify type is missing the optional field customMetrics containing all the custom metrics defined for a service.

Proposal

I would propose to add it, so that it is not necessary to extend the type to use custom metrics when they are enabled.
This could be achieved editing DecoratedFastify interface, adding the following field definition:

...
customMetrics?: Record<string, Metric<string>>
...

Your environment

node: v16
npm: 8.5.0

custom-plugin-lib: v4.3.2