Fix mode conversion with config_map volume items

[pdecat]

I added a test case that reveals an issue with config_map volume items mode:

make testacc TEST=./kubernetes/ TESTARGS='-run=TestAccKubernetesPod_with_cfg_map_volume_mount'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./kubernetes/ -v -run=TestAccKubernetesPod_with_cfg_map_volume_mount -timeout 120m
=== RUN   TestAccKubernetesPod_with_cfg_map_volume_mount
--- FAIL: TestAccKubernetesPod_with_cfg_map_volume_mount (3.17s)testing.go:449: Step 0 error: Error applying: 1 error(s) occurred:
                * kubernetes_pod.test: 1 error(s) occurred:

                * kubernetes_pod.test: spec.0.volume.1.config_map.0.items.0.mode: '' expected type 'int', got unconvertible type '*int32'
        testing.go:509: Error destroying resource! WARNING: Dangling resources
                may exist. The full state and error is shown below.

                Error: Error refreshing: 1 error(s) occurred:
* kubernetes_pod.test: 1 error(s) occurred:

                * kubernetes_pod.test: kubernetes_pod.test: spec.0.volume.1.config_map.0.items.0.mode: '' expected type 'int', got unconvertible type '*int32'

                State: <nil>
FAIL
exit status 1
FAIL    github.com/terraform-providers/terraform-provider-kubernetes/kubernetes 3.330s
GNUmakefile:15: recipe for target 'testacc' failed
make: *** [testacc] Error 1

[pdecat]

Test results with the fix

# make testacc TEST=./kubernetes/ TESTARGS='-run=TestAccKubernetes
Pod_with_cfg_map_volume_mount'                
==> Checking that code complies with gofmt requirements...                                   
TF_ACC=1 go test ./kubernetes/ -v -run=TestAccKubernetesPod_with_cfg_map_volume_mount -timeout 120m                                                                                       
=== RUN   TestAccKubernetesPod_with_cfg_map_volume_mount
--- PASS: TestAccKubernetesPod_with_cfg_map_volume_mount (5.48s)
PASS
ok      github.com/terraform-providers/terraform-provider-kubernetes/kubernetes 5.729s

[radeksimko]

Thanks for the fix and attached test @pdecat 👍
LGTM.