Project imports unconditionally enqueue an `ElasticCommitIndexerWorker`

Summary

Spotted while working on gitlab-com/gl-infra/production#800 (closed)

Steps to reproduce

Set up an elasticsearch-enabled GitLab instance with the following settings:

• elasticsearch_indexing: true
• elasticsearch_limit_indexing: true
• ElasticsearchIndexed{Namespace,{Project}.count => 0

What is the current bug behavior?

Every time a project is imported, an ElasticCommitIndexerWorker is unconditionally enqueued

What is the expected correct behavior?

Since we should be indexing zero projects with this setup, zero ElasticCommitIndexerWorker jobs should be enqueued.

Output of checks

This bug happens on GitLab.com

Possible fixes

The issue is here: https://gitlab.com/gitlab-org/gitlab-ee/blob/master/ee/app/models/ee/project_import_state.rb#L68

We need to check project.use_elasticsearch? before enqueuing the job.

Since we check it inside ElasticCommitIndexerWorker#perform, this bug is almost free - it just creates a constant level of no-op sidekiq jobs that must be discarded. We're not blocked on it for GitLab.com, but we'll benefit, resource and clarity-wise, from fixing this quickly. cc @phikai