feature(googlecloudspannerreceiver): Allow specifying scraping all databases for a Spanner instance

[adinhodovic]

Component(s)

googlecloudspannerreceiver

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

I'd like to not have to specify databases for the googlecloudspannerreceiver. They're generated and would be great to just configure the collector to list all existing databases for an instance and then just scrape them.

Describe the solution you'd like

    receivers:
      googlecloudspanner:
        collection_interval: 60s
        projects:
        - instances:
            instance_id: <test>
          project_id: <test>

Alternatively adding a flag to scrape all or .*.

    receivers:
      googlecloudspanner:
        collection_interval: 60s
        projects:
        - instances:
          - databases:
            - ".*"
            // or scrapeAll config
            scrapeAll: true
            instance_id: <test>
          project_id: <test>

Would this be considered?

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners for receiver/googlecloudspanner: @dashpole @dsimil @KiranmayiB @harishbohara11. See Adding Labels via Comments if you do not have permissions to add labels yourself. For example, comment '/label priority:p2 -needs-triaged' to set the priority and remove the needs-triaged label.