Add ProvisionedPollerConfig to Kafka event source

[Demetrios-loutsios]

Changes

• Added ProvisionedPollerConfig CloudFormation docs
  • Announced here
• ProvisionedPollerConfig allows you to specify the maximum and/or minimum provisioned pollers.
• The minimum value ranges from 1 to 200, while the maximum is from 1 to 2000

Testing

Methodology

1. Packaged contents of the branch as released https://github.com/Demetrios-loutsios/serverless/releases/download/osls-3.40.1-pre-release/osls-3.40.1.tgz
2. Updated serverless.yml function for projects with a need for this config
3. Adjusted package.json to reference serverless dependency from the pre-release package link above
4. Performed a serverless deployment to the test environment

Results (event source trigger config for function in AWS console)

[mnapoli]

Sorry I missed this PR because I didn't get a notification that it wasn't in draft anymore. Let's merge, it will ship as part of the next release.