Fix issues with processes_sync

[sethboyles]

This PR fixes two issues with the process syncer:

Docker App LRPs are not deleted from Diego when diego_docker is disabled

This was a feature that was broken in this PR: #3503

Originally, disabling diego_docker was meant to stop all docker apps from being included in the process sync query, resulting them in being removed by the syncer.

This feature is documented here: https://docs.cloudfoundry.org/adminguide/docker.html#feature-flag

Deactivating the diego_docker feature flag stops all Docker-image-based apps in your deployment within a few convergence cycles, on the order of a one minute.

During #3503's performance improvement, this clause was moved out of the main query into the new subquery that happens when fetching processes for updates/desires. This meant the docker processes were never added to the array of LRPs to_delete, although they still were not considered for update/desire syncs.

ensure CNB apps are still synced if diego_docker is disabled

If diego_docker was disabled, then the query selected 'non_docker_type' processes. This queried for Buildpack processes, but excluded CNB processes.

• I have reviewed the contributing guide

• I have viewed, signed, and submitted the Contributor License Agreement

• I have made this pull request to the main branch

• [] I have run all the unit tests using bundle exec rake

• I have run CF Acceptance Tests

[sethboyles]

I'm not sure if a this subquery or two left joins like this would be more efficient:

left_join(BuildpackLifecycleDataModel.table_name, app_guid: :app_guid).
left_join(CNBLifecycleDataModel.table_name, app_guid: :app_guid).
)).

[philippthun]

Should we do the same for the feature flag docker_cnb? So that we end up with something like this?

app_guids = if !FeatureFlag.enabled?(:diego_docker) && !FeatureFlag.enabled?(:diego_cnb)
              BuildpackLifecycleDataModel.select(:app_guid)
            elsif !FeatureFlag.enabled?(:diego_docker)
              BuildpackLifecycleDataModel.select(:app_guid).union(CNBLifecycleDataModel.select(:app_guid))
            elsif !FeatureFlag.enabled?(:diego_cnb)
              BuildpackLifecycleDataModel.select(:app_guid).union(DockerLifecycleDataModel.select(:app_guid))
            end

processes = processes.where(Sequel.qualify(ProcessModel.table_name, :app_guid) => app_guids) unless app_guids.nil?