add extended fields for credential presets

[zreigz]

What this PR does / why we need it: extends credentials for extra parameters like network configuration

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #3705

preset.yaml example:
presets:
  digitalocean:
    credentials:
      - name: digitalocean
        token:
  azure:
    credentials:
      - name: azure
        tenantId:
        subscriptionId:
        clientId:
        clientSecret:
        resourceGroup:
        vnet:
        subnet:
        routeTable:
        securityGroup:
  aws:
    credentials:
      - name: aws
        accessKeyId:
        secretAccessKey:
        vpcId:
        subnetId:
        routeTableId:
        instanceProfileName:
        securityGroupID:
  openstack:
    credentials:
      - name: openstack
        username:
        password:
        tenant:
        domain: DEFAULT
        network:
        securityGroups:
        floatingIpPool:
        routerID:
        subnetID:
  hetzner:
    credentials:
      - name: default
        token:
  vsphere:
    credentials:
      - name: default
        username:
        password:
        vmNetName:
  packet:
    credentials:
      - name: default
        apiKey:
        projectId:
        billingCycle:
  gcp:
    credentials:
      - name: default
        serviceAccount:
        network:
        subnetwork:

[floreks]

/lgtm
/approve

[kubermatic-bot]

LGTM label has been added.

Git tree hash: 50e24c95db34580ed0ca94022d0febbd76532a20

[kubermatic-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: floreks

Associated issue: #3705

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• OWNERS [floreks]
• api/pkg/handler/OWNERS [floreks]

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[floreks]

/retest

[zreigz]

/retest