Fix GO Dockerfile build error on some deployments by adding missing forward slash (/) to COPY command

[phutelmyer]

Describe the change
When using the COPY command with more than one source file, the destination must be a directory and end with a forward slash (/). The original Dockerfiles for fileshot, filestream, frontend, manager, and oneshot did not include the forward slash, which would result in an error when building the Docker images (In GitHub Actions). This PR adds the missing forward slash to the COPY command, fixing the error.

Describe testing procedures
I tested the changes by building the Docker images for fileshot, filestream, frontend, manager, and oneshot both locally and using GitHub Actions. I verified that the images were built successfully and that the applications were functioning properly.

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