Use Strelka UI Docker Image in docker-compose.yml

[phutelmyer]

Describe the change
In Strelka's default docker-compose.yml file, changing the local pull and build of the Strelka UI project to a prebuilt docker image to reduce build time and potential errors when compiling the Strelka UI container.

Describe testing procedures
Built Strelka with --no-cache using the Strelka UI image referenced in this PR. Loaded http://localhost:9980/, logged in with strelka:strelka and submitted a file successfully through the Strelka pipeline.

Sample output

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