Provide a global setting to set the default network offering for Differnet network types ( L2/Isolated/Shared)

### The required feature described as a wish

Currently, there is a global setting "cloud.kubernetes.cluster.network.offering" which is set to "DefaultNetworkOfferingforKubernetesService".

When a user executes the api (createKubernetesCluster) and doesn't provide a network, cloudstack uses the global setting value to automatically create a network based on the network offering

https://cloudstack.apache.org/api/apidocs-4.22/apis/createKubernetesCluster.html

Similarly, when a user executes the deployVirtualMachine api call , cloudstack uses the offerings mentioned in the sql query to launch vm based on the network offering

https://cloudstack.apache.org/api/apidocs-4.22/apis/deployVirtualMachine.html

deploy virtualmachine serviceofferingid=<> templateid=<> zoneid=<>

```
mysql> SELECT id, name, display_text, `default`, for_vpc FROM cloud.network_offerings WHERE availability = 'Required' AND system_only = 0;
+----+----------------------------------------------------+----------------------------------------------------------------+---------+---------+
| id | name | display_text | default | for_vpc |
+----+----------------------------------------------------+----------------------------------------------------------------+---------+---------+
| 10 | DefaultIsolatedNetworkOfferingWithSourceNatService | Offering for Isolated networks with Source Nat service enabled | 1 | 0 |
| 28 | DefaultNetworkOfferingforKubernetesService | Network Offering used for CloudStack Kubernetes service | 1 | 0 |
| 29 | DefaultNSXNetworkOfferingforKubernetesService | Network Offering for NSX CloudStack Kubernetes Service | 1 | 0 |
| 30 | DefaultNSXVPCNetworkOfferingforKubernetesService | Network Offering for NSX CloudStack Kubernetes service on VPC | 1 | 1 |
+----+----------------------------------------------------+----------------------------------------------------------------+---------+---------+
4 rows in set (0.01 sec)

```

Now if a Admin user wants to use differnet network offering as the default, he has to first mark all the offerings mentioned in the sql query as optional

Next, he has to make sure the newly created network offering as Required

```
mysql> SELECT id, name, display_text, `default`, for_vpc FROM cloud.network_offerings WHERE availability = 'Required' AND system_only = 0;
+----+------+--------------+---------+---------+
| id | name | display_text | default | for_vpc |
+----+------+--------------+---------+---------+
| 31 | test | test | 0 | 0 |
+----+------+--------------+---------+---------+
1 row in set (0.00 sec)

```

It's a tedious process and i think if CloudStack can have default global setting for each network type it would be beneficial from admin and

users who doesn't want to provide the network id during vm deployment and let cloudstack handle the network creation part

Default.isolated.network.offering
Default.shared.network.offering
Default.l2.network.offering
Default.vpc.network.offering
Default.shared.network.offering
Default.nsx.network.offering
Default.netris.network.offering

Ref

https://github.com/apache/cloudstack/issues/12116#issuecomment-3576829083

Start with the createKubernetesCluster and deployVirtualMachine API paths, the existing cloud.kubernetes.cluster.network.offering setting, and the cloud.network_offerings query shown in the issue. Determine how defaults are selected for isolated, shared, L2, VPC, NSX, and Netris networks. Done means administrators can configure distinct global defaults without changing offering availability manually, and both API flows use the appropriate configured default.

Written by the indexing model from the issue text.