[ all gcp integrations]: possibility to configure the base url

### Integration Name

Google Cloud Platform [gcp]

### Dataset Name

_No response_

### Integration Version

2.47.1

### Agent Version

9.3.0

### OS Version and Architecture

Debian 12

### User Goal

There are sovereign environments that relies on GCP technologies like S3NS in France

In this case the project-id alone is not enough to distinguished between GCP itself and partners managing gcp technologies . By default, Filebeat (and the Google SDK) will always resolve to global endpoints (e.g., [googleapis.com](http://googleapis.com/)). It will not automatically redirect to S3NS.

To ensure traffic remains within the sovereign boundary, we must make the following parameters configurable in our integrations :

- We must be able override the default endpoint googleapis.com by pointing to the S3NS URL (e.g., [pubsub.s3ns.io:443](http://pubsub.s3ns.io:443/))

- ssl.certificate_authorities: Required to trust the specific S3NS Certificate Authority (CA) chain, maybe not needed ; to confirm because S3NS is public secnum cloud french provider

### Existing Features

All GCP elastic agent integrations concerned
all filebeat and metricbeat gcp modules

### What did you see?

Not possibiliity to override the base url

### Anything else?

_No response_