Govcloud custom resource fix

[jmb12686]

What did you implement

Closes #6995 . Fix GovCloud Region ARN and Environment parsing utilities in the AWS Plugin for Custom Resources.

How can we verify it

Deploy a serverless function to us-gov-west-1 or us-gov-east-1 that uses S3 Bucket events on an existing S3 bucket, for example:

service:
  name: myService
provider:
  name: aws
  runtime: nodejs10.x
  stage: dev
  region: us-gov-west-1
functions:
  users:
    handler: users.handler
    events:
      - s3:
          bucket: legacy-photos
          event: s3:ObjectCreated:*
          rules:
            - prefix: uploads/
            - suffix: .jpg
          existing: true

Todos

Useful Scripts

• npm run test-ci --> Run all validation checks on proposed changes
• npm run lint-updated --> Lint all the updated files
• npm run lint:fix --> Automatically fix lint problems (if possible)
• npm run prettier-check-updated --> Check if updated files adhere to Prettier config
• npm run prettify-updated --> Prettify all the updated files

• Write and run all tests
• Write documentation
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[codecov-io]

Codecov Report

Merging #6996 into master will increase coverage by 0.05%.
The diff coverage is 4.76%.

@@            Coverage Diff             @@
##           master    #6996      +/-   ##
==========================================
+ Coverage   88.43%   88.48%   +0.05%     
==========================================
  Files         229      229              
  Lines        8420     8414       -6     
==========================================
- Hits         7446     7445       -1     
+ Misses        974      969       -5

Impacted Files	Coverage Δ
...ws/customResources/resources/s3/lib/permissions.js	0% <0%> (ø)	⬆️
...urces/resources/cognitoUserPool/lib/permissions.js	0% <0%> (ø)	⬆️
...rces/resources/apiGatewayCloudWatchRole/handler.js	0% <0%> (ø)	⬆️
...s/customResources/resources/eventBridge/handler.js	0% <0%> (ø)	⬆️
...stomResources/resources/cognitoUserPool/handler.js	0% <0%> (ø)	⬆️
...Resources/resources/eventBridge/lib/permissions.js	0% <0%> (ø)	⬆️
...lugins/aws/customResources/resources/s3/handler.js	0% <0%> (ø)	⬆️
lib/plugins/aws/customResources/resources/utils.js	21.21% <100%> (ø)	⬆️
lib/utils/downloadTemplateFromRepo.js	96.22% <0%> (-0.04%)	⬇️
...ompile/events/apiGateway/lib/method/integration.js	98.14% <0%> (ø)	⬆️
... and 1 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8e022ba...67d8478. Read the comment docs.

[medikoo]

@jmb12686 great thanks for proposal! We definitely should sort this out, still please see my comments

[jmb12686]

I made the modifications requested. I also found 3 additional locations under the /lib/plugins/aws/customResources/resources/* tree that were not properly handling AWS Partition for US GovCloud. I went ahead and created a utility function to properly parse from Region -> Partition for the permissions.js scripts.

[jmb12686]

I was able to test this PR's changes successfully in us-gov-west-1 region with the scenario I reported in bug #6995 . @medikoo Let me know if there's anything else I need to do to get this approved and merged into master.
Thanks.

[medikoo]

Thank you @jmb12686 it looks great!

I've just proposed one improvement, which should allow us to also resolve partition in all cases via getEnvironment and not try to assume it from region (which doesn't seem 100% bulletproof)

[jmb12686]

@medikoo I've updated the PR with the latest changes you requested.

[medikoo]

Looks great! Thank you @jmb12686

I've run it against our integration tests, and all works as expected