Allow setting custom monitored resources in the googlecloudexporter

[ridwanmsharif]

Component(s)

exporter/googlecloud

Is your feature request related to a problem? Please describe.

For some resources it would be nice if the configuration would allow us to set the monitored resources explicitly

https://cloud.google.com/monitoring/api/resources

Describe the solution you'd like

Config option to specify:

• Monitored resource name
• Monitored resource label mapping from OTel resource attributes

Describe alternatives you've considered

No response

Additional context

I'll send a PR if this is acceptable

[github-actions]

Pinging code owners:

• exporter/googlecloud: @aabmass @dashpole @jsuereth @punya @psx95

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[ridwanmsharif]

The exporter library already supports this: https://github.com/GoogleCloudPlatform/opentelemetry-operations-go/blob/560e9d12ab9b624fb704c5bdeb93dc83a5abb00d/exporter/collector/config.go#L98

We would just make it configurable in the exporter

[ridwanmsharif]

Alternatively we could add some desired mappings here: https://github.com/GoogleCloudPlatform/opentelemetry-operations-go/blob/90c5cf5c2da05b5b6332b626569d4ca035d2cdb6/internal/resourcemapping/resourcemapping.go#L66

And then no configuration change is needed for the users.