Add resource type "metric filter"

[miparnisari]

Issue #, if available: N/A

Description of changes: I resurrected part of this PR and applied some changes. Used the guided version of the CFN CLI.

• cfn test passes
• Ensured that some edge cases are handled, e.g. if you try to update a createOnly property, you will get a NotUpdatable error.
• Ensured that both CREATE and UPDATE make a call to READ first

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[miparnisari]

cfn test passes in the latest commit.

-            .done(this::constructResourceModelFromResponse);
+            .done(awsResponse -> ProgressEvent.<ResourceModel, CallbackContext>builder()
+                    .status(OperationStatus.SUCCESS)
+                    .resourceModel(Translator.translateFromReadResponse(awsResponse))
+                    .build());

-                .success();
+                .done(awsResponse -> ProgressEvent.<ResourceModel, CallbackContext>builder()
+                        .status(OperationStatus.SUCCESS)
+                        .resourceModel(model)
+                        .build());

I also noticed & fixed a problem in the Update handler. Theoretically, PutMetricFilter can throw ResourceNotFoundException. However in practice this doesn't happen. I had to add a call to Read before doing an Update to ensure that the resource actually exists before executing the update.

However, the integration tests are failing. I believe the Create handlers are being called twice for each test. The first call works & creates the resource but the second one fails because the resource already exists. Need to fix this now. Related to https://github.com/aws-cloudformation/aws-cloudformation-resource-providers-cloudwatch/issues/5