Describe the change
This change allows the Gatekeeper to be omitted from a Strelka deployment. The motivation here is simply to drop a dependency if a use case has no need for the Gatekeeper. This may be the case if a calling system already has a cache.

Originally implemented in: sublime-security#9. Merging this only conflicted due to adjacent comments. I did clean that change up a bit as well.

The documentation here could be updated to mention that the Gatekeeper may be omitted. And this section could mention that if Gatekeeper is to be omitted, the gatekeeper entry should be dropped from frontend.yaml.

Describe testing procedures
I removed gatekeeper from the compose file and removed the gatekeeper configuration from frontend.yaml. I then submitted a few test files and validated that they were analyzed. I also tested with gatekeeper enabled and saw no issues + added some temp logging to ensure that gatekeeper was used.

Sample output
If this change modifies Strelka's output, then please include a sample of the output here.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of and tested my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings