Add activate attribute support for fastly_service_waf_configuration resource

[smaeda-ks]

#529

The overall implementation follows the almost same approach as base_fastly_service_v1

% FASTLY_API_KEY=REDACTED make testacc TESTARGS='-run=TestAccFastlyServiceWAFVersionV1.*'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test -count=1 $(go list ./... |grep -v 'vendor') -v -run=TestAccFastlyServiceWAFVersionV1.* -parallel=4 -timeout 360m -ldflags="-X=github.com/fastly/terraform-provider-fastly/version.ProviderVersion=acc"
?   	github.com/fastly/terraform-provider-fastly	[no test files]
=== RUN   TestAccFastlyServiceWAFVersionV1FlattenWAFActiveRules
--- PASS: TestAccFastlyServiceWAFVersionV1FlattenWAFActiveRules (0.00s)
=== RUN   TestAccFastlyServiceWAFVersionV1AddUpdateDeleteRules
=== PAUSE TestAccFastlyServiceWAFVersionV1AddUpdateDeleteRules
=== RUN   TestAccFastlyServiceWAFVersionV1FlattenWAFRuleExclusions
--- PASS: TestAccFastlyServiceWAFVersionV1FlattenWAFRuleExclusions (0.00s)
=== RUN   TestAccFastlyServiceWAFVersionV1Validation
=== PAUSE TestAccFastlyServiceWAFVersionV1Validation
=== RUN   TestAccFastlyServiceWAFVersionV1AddUpdateDeleteExclusions
=== PAUSE TestAccFastlyServiceWAFVersionV1AddUpdateDeleteExclusions
=== RUN   TestAccFastlyServiceWAFVersionV1DetermineVersion
--- PASS: TestAccFastlyServiceWAFVersionV1DetermineVersion (0.00s)
=== RUN   TestAccFastlyServiceWAFVersionV1Add
=== PAUSE TestAccFastlyServiceWAFVersionV1Add
=== RUN   TestAccFastlyServiceWAFVersionV1AddExistingService
=== PAUSE TestAccFastlyServiceWAFVersionV1AddExistingService
=== RUN   TestAccFastlyServiceWAFVersionV1Update
=== PAUSE TestAccFastlyServiceWAFVersionV1Update
=== RUN   TestAccFastlyServiceWAFVersionV1Delete
=== PAUSE TestAccFastlyServiceWAFVersionV1Delete
=== RUN   TestAccFastlyServiceWAFVersionV1Import
=== PAUSE TestAccFastlyServiceWAFVersionV1Import
=== CONT  TestAccFastlyServiceWAFVersionV1AddUpdateDeleteRules
=== CONT  TestAccFastlyServiceWAFVersionV1AddExistingService
=== CONT  TestAccFastlyServiceWAFVersionV1Import
=== CONT  TestAccFastlyServiceWAFVersionV1Delete
--- PASS: TestAccFastlyServiceWAFVersionV1Import (126.39s)
=== CONT  TestAccFastlyServiceWAFVersionV1AddUpdateDeleteExclusions
--- PASS: TestAccFastlyServiceWAFVersionV1AddExistingService (143.18s)
=== CONT  TestAccFastlyServiceWAFVersionV1Add
--- PASS: TestAccFastlyServiceWAFVersionV1Delete (148.27s)
=== CONT  TestAccFastlyServiceWAFVersionV1Update
--- PASS: TestAccFastlyServiceWAFVersionV1AddUpdateDeleteRules (177.35s)
=== CONT  TestAccFastlyServiceWAFVersionV1Validation
--- PASS: TestAccFastlyServiceWAFVersionV1Validation (1.04s)
--- PASS: TestAccFastlyServiceWAFVersionV1Add (92.31s)
--- PASS: TestAccFastlyServiceWAFVersionV1AddUpdateDeleteExclusions (173.55s)
--- PASS: TestAccFastlyServiceWAFVersionV1Update (229.02s)
PASS
ok  	github.com/fastly/terraform-provider-fastly/fastly	378.177s
?   	github.com/fastly/terraform-provider-fastly/fastly/hashcode	[no test files]
?   	github.com/fastly/terraform-provider-fastly/version	[no test files]