allow optional labels on generated Job template

[zswanson]

Fixes #6
Adds an additional field to the Migration CRD spec labels that are copied to the migration Job's template metadata. This allows the Job's Pod to match against other controllers in the cluster that may be required - in my case I needed the migrator to match both an EKS IRSA and a PodSecurityPolicy

I wasn't sure about adding a new field for labels or just using the metadata that might be on the Migration CRD itself, but figured the specific field was more clear on usage.

GIthub workflow tests are broken until #7 is merged

20:02:29 ❯ make test
go/bin//controller-gen object:headerFile="hack/boilerplate.go.txt" paths="./..."
go fmt ./...
api/v1beta1/migrator_types.go
api/v1beta1/zz_generated.deepcopy.go
go vet ./...
go/bin//controller-gen "crd:trivialVersions=true" rbac:roleName=manager-role webhook paths="./..." output:crd:artifacts:config=config/crd/bases
go test ./... -coverprofile cover.out
?   	github.com/coderanger/migrations-operator	[no test files]
?   	github.com/coderanger/migrations-operator/api/v1beta1	[no test files]
?   	github.com/coderanger/migrations-operator/cmd/waiter	[no test files]
ok  	github.com/coderanger/migrations-operator/components	0.635s	coverage: 76.6% of statements
ok  	github.com/coderanger/migrations-operator/controllers	11.401s	coverage: 100.0% of statements
ok  	github.com/coderanger/migrations-operator/http	7.388s	coverage: 83.3% of statements
ok  	github.com/coderanger/migrations-operator/integration	0.878s	coverage: [no statements]
?   	github.com/coderanger/migrations-operator/utils	[no test files]
ok  	github.com/coderanger/migrations-operator/webhook	7.524s	coverage: 85.3% of statements
32.43s user 26.22s system 258% cpu 22.666s total