Dokku uses a few external images for various bits of functionality, but these must be manually updated every so often due to being referenced in code.
By moving the references to Dockerfiles, we can take advantage of dependabot to issue automatic PRs when they are out of date.
Using compose instead of manual docker calls allows folks to customize the vector container by using a custom compose.yml template file. This opens us up to more customizations while aligning container management with how we do other external containers (such as for the proxy plugins).
Refs #5784
Not all properties can be set globally, and the "appName" in the global case is currently defaulted to `--global`. This is okay because domain label names cannot start with hyphens, and all app names must be valid domain label names.
