[Google Cloud Platform]: Credentials fields are not typed as secret/password

### Integration Name

Google Cloud Platform [gcp]

### Integration Version

2.4.2

When configuring the GCP integration, both options for credential files are in plain-text:

If you look at Google Security Command Center, for instance, the credentials are correctly flagged as a password/secret field

For reference:

https://github.com/elastic/integrations/blob/main/packages/gcp/manifest.yml#L40-L51

```
- name: credentials_file
type: text
title: Credentials File
multi: false
required: false
show_user: true
- name: credentials_json
type: text
title: Credentials Json
multi: false
required: false
show_user: true
```

https://github.com/elastic/integrations/blob/main/packages/google_scc/manifest.yml#L71-L78

```
- name: credentials
type: password
title: Credentials JSON/File
multi: false
required: false
show_user: true
description: "Path to a JSON or JSON blob file containing the credentials and key used to subscribe. Note: This is required field if not installed in GCP-Cloud Environment."
secret: true
```

Is worth having the GCP integration apply the same field format to the credentials?