Fully refactor the entire codebase.

[knadh]

Fully refactor the entire codebase.

• Split and cleanly separate the main package into relay/producer/source_pool controllers.
• Restructure files and internal packages.
• Rewrite, simplify, and detatch polling and healthcheck logic spread across relay and consumer sources into cleaner abstractions.
• Simplify relay to only do relaying and not handle server management.
• Rewrite the old multi-config based consumer into a new "source pool" controller that acts like a connection pool and hides away all server management and healthcheck complexities.
• Remove and simplify redundant util methods structs.
• Simplify and rewrite orchestration logic in multiple places: relay, source pool management, healthchecks.
• Simplify config structure and config initialization across controllers.
• Simplify main.go to do initialization and composition only.

[joeirimpan]

Can you rebase with develop and raise it to develop?