Fix minor errors in the GCP service documentation

[jotacarma90]

Description

Hi team, working on issue #15100, related to GCP service e2e tests, I have found some things that could be clarified.

• Creating a service account:

  • To add the Storage Legacy Bucket Writer role you need to have first created a custom role with its same permissions. There is an issue associated with this problem.

• Some examples shown on the Wazuh configuration related to gcp-bucket show some tags that should not, such as project_id and subscription_name:

  • https://documentation.wazuh.com/current/gcp/prerequisites/credentials.html#using-an-authentication-file
  • https://documentation.wazuh.com/current/user-manual/reference/ossec-conf/gcp-bucket.html#configuration-example

[CarlosRS9]

The issue with the Storage Legacy Bucket write role will be reviewed and fixed in #4996.

The reference pages for gcp-bucket and gcp-pubsub will be reviewed and updated in #5699.