feat: Support context for all Nutanix client calls

[dlipovetsky]

What problem does this PR solve?:
This allows us to handle context cancellation when using the Nutanix v4 go client, which itself does not support context. That, together with #1235, allows us to return check results before the API server webhook timeout. This means the client sees results, instead of an uninformative (and misleading) "failed to call webhook" error.

Before

Notice that no results are returned.

│ kubectl apply --dry-run=server -f invalid-bad-prismcentral-url.yaml -v=4
I0723 12:12:17.523594 2625398 envvar.go:172] "Feature gate default state" feature="ClientsPreferCBOR" enabled=false
I0723 12:12:17.523624 2625398 envvar.go:172] "Feature gate default state" feature="InformerResourceVersion" enabled=false
I0723 12:12:17.523627 2625398 envvar.go:172] "Feature gate default state" feature="InOrderInformers" enabled=true
I0723 12:12:17.523630 2625398 envvar.go:172] "Feature gate default state" feature="WatchListClient" enabled=false
I0723 12:12:17.523633 2625398 envvar.go:172] "Feature gate default state" feature="ClientsAllowCBOR" enabled=false
I0723 12:12:27.582271 2625398 helpers.go:246] server response object: %s[{
  "kind": "Status",
  "apiVersion": "v1",
  "metadata": {},
  "status": "Failure",
  "message": "error when creating \"invalid-bad-prismcentral-url.yaml\": Internal error occurred: failed calling webhook \"preflight.cluster.caren.nutanix.com\": failed to call webhook: Post \"https://cluster-api-runtime-extensions-nutanix-admission.default.svc:443/preflight-v1beta1-cluster?timeout=10s\": context deadline exceeded",
  "reason": "InternalError",
  "details": {
    "causes": [
      {
        "message": "failed calling webhook \"preflight.cluster.caren.nutanix.com\": failed to call webhook: Post \"https://cluster-api-runtime-extensions-nutanix-admission.default.svc:443/preflight-v1beta1-cluster?timeout=10s\": context deadline exceeded"
      }
    ]
  },
  "code": 500
}]
Error from server (InternalError): error when creating "invalid-bad-prismcentral-url.yaml": Internal error occurred: failed calling webhook "preflight.cluster.caren.nutanix.com": failed to call webhook: Post "https://cluster-api-runtime-extensions-nutanix-admission.default.svc:443/preflight-v1beta1-cluster?timeout=10s": context deadline exceeded

After

Notice that the results are returned.

│ kubectl apply --dry-run=server -f invalid-bad-prismcentral-url.yaml -v=4
I0723 12:06:59.458667 2603987 envvar.go:172] "Feature gate default state" feature="ClientsAllowCBOR" enabled=false
I0723 12:06:59.458703 2603987 envvar.go:172] "Feature gate default state" feature="ClientsPreferCBOR" enabled=false
I0723 12:06:59.458706 2603987 envvar.go:172] "Feature gate default state" feature="InformerResourceVersion" enabled=false
I0723 12:06:59.458709 2603987 envvar.go:172] "Feature gate default state" feature="InOrderInformers" enabled=true
I0723 12:06:59.458711 2603987 envvar.go:172] "Feature gate default state" feature="WatchListClient" enabled=false
I0723 12:07:07.583019 2603987 helpers.go:246] server response object: %s[{
  "kind": "Status",
  "apiVersion": "v1",
  "metadata": {},
  "status": "Failure",
  "message": "error when creating \"invalid-bad-prismcentral-url.yaml\": admission webhook \"preflight.cluster.caren.nutanix.com\" denied the request: preflight checks failed due to an internal error",
  "reason": "InternalError",
  "details": {
    "causes": [
      {
        "reason": "NutanixCredentials",
        "message": "Failed to validate credentials: Get \"https://example.com:9441/api/nutanix/v3/users/me\": context deadline exceeded. This is usually a temporary error. Please retry.",
        "field": "$.spec.topology.variables[?@.name==\"clusterConfig\"].value.nutanix.prismCentralEndpoint"
      }
    ]
  },
  "code": 500
}]
Error from server (InternalError): error when creating "invalid-bad-prismcentral-url.yaml": admission webhook "preflight.cluster.caren.nutanix.com" denied the request: preflight checks failed due to an internal error

Which issue(s) this PR fixes:
Fixes #

How Has This Been Tested?:

Special notes for your reviewer:

[dkoshkin]

Nice solution!

[thunderboltsid]

lgtm