Cannot create Google-managed SSL

##### SUMMARY

Create certificate API not support to create Google-managed SSL.

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME

gcp_compute_ssl_certificate

##### ADDITIONAL INFORMATION

Currently `gcp_compute_ssl_certificate` only support SSL creation using external key. Sadly, cannot create SSL using feature Google-managed certificate. I suggest to add 2 new variables:
- managed (dict)
- type: (str)

And remove required attribute from 2 parameters:
- certificate
- privateKey

based on Google Cloud Platform Document: https://cloud.google.com/compute/docs/reference/rest/v1/sslCertificates/insert

Implementation https://github.com/ansible-collections/google.cloud/pull/672

```yaml
---
- name: Create a Google-managed SSL Certificate
google.cloud.gcp_compute_ssl_certificate:
name: "dpanel-terpusat-com"
description: "cloud.terpusat.com Google-managed Certificate"
type: "MANAGED"
managed:
domains:
- cloud.terpusat.com
project: "terpusat-dpanel"
auth_kind: "serviceaccount"
service_account_file: "./credential.json"
state: present
```

Start at the gcp_compute_ssl_certificate component and read the linked implementation pull request #672 alongside the Google Cloud sslCertificates insert documentation. Check how the proposed managed and type inputs relate to certificate and privateKey, then verify that the YAML example can create a Google-managed certificate and that the module's existing checks remain covered.

Written by the indexing model from the issue text.