[BUG]: SidecarEgressMap.Get() throws concurrent map access error intermittently

[shriramsharma]

Describe the bug
SidecarEgressMap.Get() throws concurrent map access error intermittently.
The map access inside the func is not thread-safe.

admiral/admiral/pkg/controller/common/types.go

Line 179 in 72d5ec4

func (s *SidecarEgressMap) Get(key string) map[string]SidecarEgress {

Steps To Reproduce
This error is pretty intermittent. I wrote a test to reproduce this error.

func TestSidecarEgressGet(t *testing.T) {

	egressMap := NewSidecarEgressMap()
	egressMap.Put("pkey1", "pkey2", "fqdn", map[string]string{"pkey2": "pkey2"})

	ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(5*time.Second))
	defer cancel()

	go func(ctx context.Context) {
		for {
			select {
			case <-ctx.Done():
				return
			default:
				egressMap.Put("pkey1", string(uuid.NewUUID()), "fqdn", map[string]string{"pkey2": "pkey2"})
			}
		}
	}(ctx)

	for {
		select {
		case <-ctx.Done():
			return
		default:
			assert.NotNil(t, egressMap.Get("pkey1"))
		}
	}

}

Error:

fatal error: concurrent map read and map write

goroutine 10 [running]:
runtime.throw({0x181ef9c, 0xc000495980})
	/Users/ssharma34/shriram/sandbox/goroots/go1.17/src/runtime/panic.go:1198 +0x71 fp=0xc000083e70 sp=0xc000083e40 pc=0x1036df1
runtime.mapaccess1_faststr(0xc0001127e0, 0xc000203a00, {0x180b471, 0x5})
	/Users/ssharma34/shriram/sandbox/goroots/go1.17/src/runtime/map_faststr.go:21 +0x3a5 fp=0xc000083ed8 sp=0xc000083e70 pc=0x1014045
github.com/istio-ecosystem/admiral/admiral/pkg/controller/common.(*SidecarEgressMap).Get(...)
	/Users/ssharma34/shriram/personal/github/admiral/admiral/pkg/controller/common/types.go:180

Expected behavior
Have a mutex around the map for synchronized access.