From the official Docker Hub image page:
Bitbucket Server is an on-premises source code management solution for Git that's secure, fast, and enterprise grade. Create and manage repositories, set up fine-grained permissions, and collaborate on code - all with the flexibility of your servers.
Learn more about Bitbucket Server: https://www.atlassian.com/software/bitbucket/server
You can find the repository for this Dockerfile at https://hub.docker.com/r/atlassian/bitbucket-server
The deploy.yaml uses the official Docker image to deploy a basic configuration of Bitbucket Server on Akash.