adding basic yara functionality by default

[Derekt2]

Describe the change
Adds a rules.yara file to the backend, and mounts the file in the backend's /etc/yara directory to ensure there is at least one rule. Yara rules can be added without having to rebuild the container, just must restart before rescanning a file.

Describe testing procedures
I ran built strelka before and after changes to verify it works as intended.

Sample output
Changes the scan yara from "compiling error" to show the test rule result.
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

[Derekt2]

[phutelmyer]

No issues when building / testing.
Thanks @Derekt2!