Adding client oneshot Dockerfile

[phutelmyer]

Describe the change
Strelka oneshot required a go build and did not support Docker (unlike fileshot). Implemented a Dockerfile.

Describe testing procedures

1. Cloned the repository

   git clone https://github.com/target/strelka.git /opt/strelka/

2. Built the container

   cd /opt/strelka/
   docker build -f build/go/oneshot/Dockerfile -t strelka-oneshot .

Sample output
N/A

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