maint: Refactor Config

[MikeGoldsmith]

Which problem is this PR solving?

Config options were scattered through the codebase. This PR centralises all configuration options into the Config package and updates usage to be consistent.

Short description of the changes

• Move config vars into NewConfig
• Remove flags.* usage
• Add descriptions to Config struct fields
• Move stats dataset name from assembler to config
• Add stats dataset config option and allow to read from env var
• Removes unused config options - max, statsevery, verbose, debug, quiet, fname and tstype
• Add config validate func with Missing and Invalid error types
• Add GetMaskedAPIKey func to config so we can safely log it
• Add tests for key masking
• Add env util for retrieving string and bool env vars with a default
• Reorganise main.go, includes setup of logging, libhoney and k8s into their own funcs
• Update README to include the env vars we currently support
• Add test and docker-test makefile targets
• Update main and pr github workflows to execute tests using new makefile targets

How to verify that this has the expected result

Config usage is much cleaner and easier to reason about.

Environment variables set in the k8s deployment are used when configuring the agent. For example, you can set HONEYCOMB_DATASET=some-other-place under env.

[robbkidd]

To get the env-var lookups working, I think we'll need to refactor further to remove the flag.* usage in favor of doing more in the NewConfig constructor or wrap the var x = flag.* statements in an init() {} function.

[JamieDanielson]

This is great, thanks Mike! I updated these environment variables in my .env file and updated my deployment.yaml and confirmed the updated values.

# .env
HONEYCOMB_API_KEY=<redacted>
HONEYCOMB_DATASET=jamie-agent
HONEYCOMB_STATS_DATASET=jamie-agent-stats
...

# deployment.yaml
            - name: HONEYCOMB_DATASET
              value: $HONEYCOMB_DATASET
            - name: HONEYCOMB_STATS_DATASET
              value: $HONEYCOMB_STATS_DATASET

2023-09-19 11:20:31 3:20PM INF Starting Honeycomb Network Agent agent_version=0.0.16-alpha api_key=******************1234 dataset=jamie-agent endpoint=https://api.honeycomb.io stats_dataset=jamie-agent-stats

[JamieDanielson]

Updated the debug service start in main to use the computed config object , realized that was missing in testing with my environment variable testing. Also added a few clarifications and changes to the deployment yamls! Think this should be good to go now!