[WIP] Add a way to overwrite existing disable task cluster requests

[serbay-stripe]

Context

At Stripe, we're looking to use blue-green deploys for the mantis agents and have drafted a workflow that goes as below. This PR adds the capability to enable a set of agents that were previously disabled using a DisableTaskExecutorsRequest. This is done through adding an optional field overwriteExisting to the request. I tried to keep the changes minimal and backwards compatible. If the overwriteExisting is missing in the request, everything should behave as it did before.

The orchestration workflow we have drafted is as follows:

• Let's assume we have a blue stack deployed for mantis agents.
• We deploy the new version of the mantis agents as a new stack we'll call green.
• Issue a request to expire the existing / active "disable requests" for the green stack using a request similar to the one below:

  curl -L \
  --header "Content-Type: application/json" \
  --header "Accept: application/json" \
  --data '{"attributes": {"asg_name": "green-asg-identifier"}, "overwriteExisting": true, "expirationDurationInHours": "0"}' \
  http://master.service/api/v1/resourceClusters/DEFAULT_CLUSTER/disableTaskExecutors

This kicks off the part of the code that issues ExpireDisableTaskExecutorsRequest and removes the DisableTaskExecutorsRequest stored as we have the overwriteExisting set to true.

• Issue a request to disable the blue stack

  curl -L \
  --header "Content-Type: application/json" \
  --header "Accept: application/json" \
  --data '{"attributes": {"asg_name": "blue-asg-identifier"}, "overwriteExisting": true, "expirationDurationInHours": "non-zero-value-that-wont-expire-soon"}' \
  http://master.service/api/v1/resourceClusters/DEFAULT_CLUSTER/disableTaskExecutors

• Wait until the workloads / jobs move to the green stack to finalize the deployment.

Checklist

• [ ] ./gradlew build compiles code correctly
• [x] Added new tests where applicable
• [ ] ./gradlew test passes all tests
• [ ] Extended README or added javadocs where applicable