fix(metrics): only add required artifacts to application

[nflaig]

This PR resolves three issues of the component:

1. The component adds MetricsPushObserver even if it is not configured
2. Providing custom config was overwriting whole default config instead of merging

Checklist

• DCO (Developer Certificate of Origin) signed in all commits
• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• API Documentation in code was updated

[raymondfeng]

It can be simplified as:

if (!options.defaultMetrics?.disabled) {

[nflaig]

its actually not the same if options.pushGateway is undefined it will be true whereas options.pushGateway && !options.pushGateway.disabled is false becasue !undefined === true

[raymondfeng]

if (options.defaultMetrics?.disabled !== true) is probably the simplest.

[nflaig]

this does not work in case of the pushGateway which is undefined and we dont want to add the MetricsPushObserver in that case

[raymondfeng]

@nflaig Please rebase against latest master to resolve conflicts.

[nflaig]

@raymondfeng I removed some changes from the PR and only added the fix now to not add the MetricsPushObserver if pushGateway is not configured and the fact that the config was overwritten instead of merged.

The other consideration was to add options.methodInvocations to enable/disable those or as already discussed in the health component, it could be considered to add a options.disabled to completely disable the component although this could also be achieved by wrapping app.component into an if-statement