Invalid label causes panic in Python SDK

[lblackstone]

import pulumi
from pulumi_kubernetes.core.v1 import Pod

pod = Pod(
    "foo",
    metadata={"labels": "foo"},
    spec={"containers": [{"name": "nginx", "image": "nginx"}]}
)

causes the following panic:

    panic: interface conversion: interface {} is string, not map[string]interface {}
    goroutine 133 [running]:
    github.com/pulumi/pulumi-kubernetes/pkg/metadata.SetLabel(...)
    	/Users/levi/go/src/github.com/pulumi/pulumi-kubernetes/pkg/metadata/labels.go:31
    github.com/pulumi/pulumi-kubernetes/pkg/metadata.SetManagedByLabel(...)
    	/Users/levi/go/src/github.com/pulumi/pulumi-kubernetes/pkg/metadata/labels.go:40
    github.com/pulumi/pulumi-kubernetes/pkg/provider.(*kubeProvider).Check(0xc0004dc600, 0x257c880, 0xc00137e3c0, 0xc001380000, 0xc0004dc600, 0x213bd01, 0xc001380080)
    	/Users/levi/go/src/github.com/pulumi/pulumi-kubernetes/pkg/provider/provider.go:273 +0x16b0
    github.com/pulumi/pulumi-kubernetes/vendor/github.com/pulumi/pulumi/sdk/proto/go._ResourceProvider_Check_Handler.func1(0x257c880, 0xc00137e3c0, 0x226f200, 0xc001380000, 0x228e6a0, 0x340dcf8, 0x257c880, 0xc00137e3c0)
    	/Users/levi/go/src/github.com/pulumi/pulumi-kubernetes/vendor/github.com/pulumi/pulumi/sdk/proto/go/provider.pb.go:1303 +0x86
    github.com/pulumi/pulumi-kubernetes/vendor/github.com/grpc-ecosystem/grpc-opentracing/go/otgrpc.OpenTracingServerInterceptor.func1(0x257c880, 0xc00137e000, 0x226f200, 0xc001380000, 0xc001378020, 0xc001378040, 0x0, 0x0, 0x253dc20, 0xc0004e5d60)
    	/Users/levi/go/src/github.com/pulumi/pulumi-kubernetes/vendor/github.com/grpc-ecosystem/grpc-opentracing/go/otgrpc/server.go:61 +0x360
    github.com/pulumi/pulumi-kubernetes/vendor/github.com/pulumi/pulumi/sdk/proto/go._ResourceProvider_Check_Handler(0x22900e0, 0xc0004dc600, 0x257c880, 0xc00137e000, 0xc00137c000, 0xc00044d180, 0x257c880, 0xc00137e000, 0xc00137a000, 0xc8)
    	/Users/levi/go/src/github.com/pulumi/pulumi-kubernetes/vendor/github.com/pulumi/pulumi/sdk/proto/go/provider.pb.go:1305 +0x158
    github.com/pulumi/pulumi-kubernetes/vendor/google.golang.org/grpc.(*Server).processUnaryRPC(0xc0004cf500, 0x2597b40, 0xc0004b2300, 0xc000012100, 0xc000137f50, 0x33dec60, 0x0, 0x0, 0x0)
    	/Users/levi/go/src/github.com/pulumi/pulumi-kubernetes/vendor/google.golang.org/grpc/server.go:972 +0x470
    github.com/pulumi/pulumi-kubernetes/vendor/google.golang.org/grpc.(*Server).handleStream(0xc0004cf500, 0x2597b40, 0xc0004b2300, 0xc000012100, 0x0)
    	/Users/levi/go/src/github.com/pulumi/pulumi-kubernetes/vendor/google.golang.org/grpc/server.go:1252 +0xda6
    github.com/pulumi/pulumi-kubernetes/vendor/google.golang.org/grpc.(*Server).serveStreams.func1.1(0xc0000ee090, 0xc0004cf500, 0x2597b40, 0xc0004b2300, 0xc000012100)
    	/Users/levi/go/src/github.com/pulumi/pulumi-kubernetes/vendor/google.golang.org/grpc/server.go:691 +0x9f
    created by github.com/pulumi/pulumi-kubernetes/vendor/google.golang.org/grpc.(*Server).serveStreams.func1
    	/Users/levi/go/src/github.com/pulumi/pulumi-kubernetes/vendor/google.golang.org/grpc/server.go:689 +0xa1

Labels should be a dict rather than a string (e.g. "labels": {"foo": "true"}, not "labels": "foo"), but this error should be caught before it causes a panic in the provider.

[hausdorff]

Not 100% we're on the same page when we say "before it causes a panic with the provider", but SetLabels should return an error if it can't set labels because labels are mistyped. We should not try to inject typing logic into the SDK.