feat: bootstrap and graceful shutdown

[moreirathomas]

Description

Breaks main in many methods for a more granular configuration. Offers:

• configurable graceful shutdown procedure with shutdown package.
• config struct defining the program variable configuration (à la 12 factors app), config is read from file with default being .env. Accepts one single flag: config to provide the path to the config file.

Changes

Refactor cmd/main.

Update golangci-yml:

• use camelCase check names (for yaml reference intellisense)
• increase min cognitive complexity report from 8 to 15 (recommended is between 10 and 20, so right in the middle)

Notes

Coses #14

[moreirathomas]

The main thing is:

In order to be able to call Server.Shutdown(ctx) and RequestService.Close(), we need to have Server.ListenAndServe to not be blocking.

Server.Shutdown(ctx) must be called while Server.ListenAndServe runs in a goroutine.

Only after Server.ListenAndServe internally gets the interrupt and return http.ErrServerClosed and we can safely exit the program.

My solution was to:

• put Server.ListenAndServe inside a goroutine
• return the callback to gracefully stop the server when any interrupt signal is received (manual ctrl+c or some redeployment trigger from our hosting service)

In other words: run launches the server in a thread and returns a way to gracefully stop it from the parent. Any error returned is a fatal error during launch.

Although I agree that shutdown.Handle may be too much.

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Also, you raised good points regarding the env vars injections on real world deployment too. We might need to think about that.