Implements kms(cmk) alias

[haarchri]

Description of your changes

Implements kms(cmk) alias

Fixes #778

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

➜  provider-aws git:(kms-alias) ✗ kubectl apply -f examples/kms/alias.yaml
alias.kms.aws.crossplane.io/dev-key created

➜  provider-aws git:(kms-alias) ✗ kubectl get alias
NAME      READY   SYNCED   EXTERNAL-NAME
dev-key   True    True     alias/dev-key

➜  provider-aws git:(kms-alias) ✗ kubectl describe alias dev-key
Name:         dev-key
Namespace:    
Labels:       <none>
Annotations:  crossplane.io/external-name: alias/dev-key
API Version:  kms.aws.crossplane.io/v1alpha1
Kind:         Alias
Metadata:
  Creation Timestamp:  2021-07-26T21:49:35Z
  Finalizers:
    finalizer.managedresource.crossplane.io
  Generation:        2
  Resource Version:  1975464
  Self Link:         /apis/kms.aws.crossplane.io/v1alpha1/aliases/dev-key
  UID:               36159cba-4325-48f7-a3d8-964be025676c
Spec:
  Deletion Policy:  Delete
  For Provider:
    Alias Name:     alias/dev-key
    Region:         eu-central-1
    Target Key ID:  ea87e120-8417-4ade-8499-9e093d5664d7
    Target Key ID Ref:
      Name:  dev-key
  Provider Config Ref:
    Name:  default
Status:
  At Provider:
  Conditions:
    Last Transition Time:  2021-07-26T21:49:35Z
    Reason:                ReconcileSuccess
    Status:                True
    Type:                  Synced
    Last Transition Time:  2021-07-26T21:49:35Z
    Reason:                Available
    Status:                True
    Type:                  Ready
Events:
  Type    Reason                   Age   From                                 Message
  ----    ------                   ----  ----                                 -------
  Normal  CreatedExternalResource  35s   managed/alias.kms.aws.crossplane.io  Successfully requested creation of external resource

➜  provider-aws git:(kms-alias) ✗ kubectl delete -f examples/kms/alias.yaml
alias.kms.aws.crossplane.io "dev-key" deleted

[AaronME]

Looks good! Thanks, @haarchri !

[AaronME]

Closing and re-opening to trigger tests.