Avoid container naming conflicts

[ipmb]

A client hit this error today:

Container] 2026/05/20 21:57:53.226876 Entering phase PRE_BUILD
[Container] 2026/05/20 21:57:53.228161 Running command apppack-builder prebuild
21:57:53 INF downloading build cache
2026/05/20 21:57:53 Downloading build-cache/committed/sha256:13ce45531117a86fe46f8d68258a3535f3f9cc80d07c712506619a717d3e7c00.tar to /tmp/apppack-cache/build-cache/committed/sha256:13ce45531117a86fe46f8d68258a3535f3f9cc80d07c712506619a717d3e7c00.tar
2026/05/20 21:57:53 Downloading build-cache/committed/io.buildpacks.lifecycle.cache.metadata to /tmp/apppack-cache/build-cache/committed/io.buildpacks.lifecycle.cache.metadata
2026/05/20 21:57:53 Downloading build-cache/committed/sha256:a36cedd8e999d7580f61c98e7f61b9c68a21411e33ecb8d9dddc36f2494a9e70.tar to /tmp/apppack-cache/build-cache/committed/sha256:a36cedd8e999d7580f61c98e7f61b9c68a21411e33ecb8d9dddc36f2494a9e70.tar
2026/05/20 21:57:53 Downloading build-cache/committed/sha256:a14f29ace7d57bac108297393f5d5f6eb03452ef54a54baef7bf7df955842e04.tar to /tmp/apppack-cache/build-cache/committed/sha256:a14f29ace7d57bac108297393f5d5f6eb03452ef54a54baef7bf7df955842e04.tar
2026/05/20 21:57:53 Downloading build-cache/committed/sha256:d5c24a5375428747e8c55cd4d103a75888111e10cdf17ba79cb76a23174bb1fe.tar to /tmp/apppack-cache/build-cache/committed/sha256:d5c24a5375428747e8c55cd4d103a75888111e10cdf17ba79cb76a23174bb1fe.tar
2026/05/20 21:57:53 Downloading build-cache/committed/sha256:be1ecc4c46d21a1fc5a77b899b7d6ba3121b8f87d7a4c483facbf1b3f9e907ec.tar to /tmp/apppack-cache/build-cache/committed/sha256:be1ecc4c46d21a1fc5a77b899b7d6ba3121b8f87d7a4c483facbf1b3f9e907ec.tar
21:57:53 INF pulling buildpack images
22: Pulling from heroku/builder
Digest: sha256:c5d8305d8431263706f49f14bbbc5fec8ebf1e99ab3dfe8e391c5b5bfe4cb116
Status: Image is up to date for registry.apppackcdn.net/heroku/builder:22
registry.apppackcdn.net/heroku/builder:22
alpine: Pulling from library/postgres
Digest: sha256:96d56f7f57c6aacd1fcb908bc83b345ec5f83231ee486dd66a1baadce274db88
Status: Image is up to date for postgres:alpine
docker.io/library/postgres:alpine
21:57:56 FTL Error error="Error response from daemon: Conflict. The container name \"/db\" is already in use by container \"6b84fe4b52a25674544419323ffef0833a1d5245ad1f16ccf0c435151399cb15\". You have to remove (or rename) that container to be able to reuse that name."
[Container] 2026/05/20 21:57:56.302253 Command did not exit successfully apppack-builder prebuild exit status 1
[Container] 2026/05/20 21:57:56.306346 Phase complete: PRE_BUILD State: FAILED
[Container] 2026/05/20 21:57:56.306363 Phase context status code: COMMAND_EXECUTION_ERROR Message: Error while executing command: apppack-builder prebuild. Reason: exit status 1

Codebuild is configured to reuse the docker daemon, but the db container that's getting setup in our prebuild phase is not getting a unique name. Let's make sure it gets a unique name (as with any other container that spins up). If for some reason that's really hard, we can disable docker daemon reuse in the Cloudformation stack.