Improvements to compose.dev.yaml

[johnstcn]

coder/coder#22157 added a development-focused Compose file (compose.dev.yaml).
The ultimate aim of this is to eventually take on most of the load of the ailing develop.sh.

Tracking requested improvements here:

• Slim down Docker images
• Support HA coderd
• Prometheus
• pprof helper
• Load balancer
• Delve debugging on port 12345
• Allow injecting .env
• How-to guide