Address CA config map creation race condition

[marc-barry]

During rapid mutation of pods with the qpoint.io/inject-ca: "true" annotation it is possible that a race condition occurs that leads to the following error:

2023-12-05T05:18:07Z	ERROR	pod.v1.admission.webhook[2e6e597f-f6b9-435d-a7bf-70f608239668]	failed to add assets to namespace for ca injection	{"error": "creating configmap for Qtap CA bundles: configmaps \"qtap-ca-bundle.crt\" already exists"}
github.com/qpoint-io/kubernetes-qtap-operator/api/v1.(*Webhook).Handle
	/workspace/api/v1/webhook.go:94
sigs.k8s.io/controller-runtime/pkg/webhook/admission.(*Webhook).Handle
	/go/pkg/mod/sigs.k8s.io/[email protected]/pkg/webhook/admission/webhook.go:169
sigs.k8s.io/controller-runtime/pkg/webhook/admission.(*Webhook).ServeHTTP
	/go/pkg/mod/sigs.k8s.io/[email protected]/pkg/webhook/admission/http.go:98
sigs.k8s.io/controller-runtime/pkg/webhook/internal/metrics.InstrumentedHook.InstrumentHandlerInFlight.func1
	/go/pkg/mod/github.com/prometheus/[email protected]/prometheus/promhttp/instrument_server.go:60
net/http.HandlerFunc.ServeHTTP
	/usr/local/go/src/net/http/server.go:2136
github.com/prometheus/client_golang/prometheus/promhttp.InstrumentHandlerCounter.func1
	/go/pkg/mod/github.com/prometheus/[email protected]/prometheus/promhttp/instrument_server.go:147
net/http.HandlerFunc.ServeHTTP
	/usr/local/go/src/net/http/server.go:2136
github.com/prometheus/client_golang/prometheus/promhttp.InstrumentHandlerDuration.func2
	/go/pkg/mod/github.com/prometheus/[email protected]/prometheus/promhttp/instrument_server.go:109
net/http.HandlerFunc.ServeHTTP
	/usr/local/go/src/net/http/server.go:2136
net/http.(*ServeMux).ServeHTTP
	/usr/local/go/src/net/http/server.go:2514
net/http.serverHandler.ServeHTTP
	/usr/local/go/src/net/http/server.go:2938
net/http.(*conn).serve
	/usr/local/go/src/net/http/server.go:2009

The issue is that the config map already exists due a a race condition with multiple calls to EnsureAssetsInNamespace() and multiple attempts to create the same config map. This pull request locks the write part of the function call so only one can be in-flight at any given time to prevent creation errors.