[receiver/googlecloudpubsub] Add config for credentials info

[PaulBernier]

Component(s)

receiver/googlecloudpubsub

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

Currently the GCP PubSub does not have any config to specify credentials information to connect to GCP. I want to add the ability to specify credentials file or credentials JSON data directly for the client to use to connect.

Describe the solution you'd like

1. Add a new config to specify the path to a credential file
2. Add a new config to specify directly credentials info (as a JSON)

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners:

• receiver/googlecloudpubsub: @alexvanboxel

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[alexvanboxel]

The receiver uses just like all Google integrations, the Google clients. Although I haven't tested this I'm assuming the clients support:

https://cloud.google.com/docs/authentication/application-default-credentials

I like to keep the receiver as consistent as possible with the Google maintained components. I like to have some input of someone from Google first. Maybe @jsuereth could give an opinion (Technical Committee).