refactor(database): move worker logic into separate package

[jbrockopp]

Based off of #574, #663 and #687

This change continues the refactor efforts initially introduced in the above PRs.

This adds a new worker package to the github.com/go-vela/server/database package.

This contains a WorkerService interface declaring all functions necessary for worker based interactions with the database:

server/database/worker/service.go

Lines 11 to 43 in 7991f03

	// WorkerService represents the Vela interface for worker
	// functions with the supported Database backends.
	//
	//nolint:revive // ignore name stutter
	type WorkerService interface {
	// Worker Data Definition Language Functions
	//
	// https://en.wikipedia.org/wiki/Data_definition_language
	// CreateWorkerIndexes defines a function that creates the indexes for the workers table.
	CreateWorkerIndexes() error
	// CreateWorkerTable defines a function that creates the workers table.
	CreateWorkerTable(string) error
	// Worker Data Manipulation Language Functions
	//
	// https://en.wikipedia.org/wiki/Data_manipulation_language
	// CountWorkers defines a function that gets the count of all workers.
	CountWorkers() (int64, error)
	// CreateWorker defines a function that creates a new worker.
	CreateWorker(*library.Worker) error
	// DeleteWorker defines a function that deletes an existing worker.
	DeleteWorker(*library.Worker) error
	// GetWorker defines a function that gets a worker by ID.
	GetWorker(int64) (*library.Worker, error)
	// GetWorkerForHostname defines a function that gets a worker by hostname.
	GetWorkerForHostname(string) (*library.Worker, error)
	// ListWorkers defines a function that gets a list of all workers.
	ListWorkers() ([]*library.Worker, error)
	// UpdateWorker defines a function that updates an existing worker.
	UpdateWorker(*library.Worker) error
	}

This package also contains the engine which implements the above service interface:

server/database/worker/worker.go

Lines 23 to 37 in 7991f03

	// engine represents the worker functionality that implements the WorkerService interface.
	engine struct {
	// engine configuration settings used in worker functions
	config *config
	// gorm.io/gorm database client used in worker functions
	//
	// https://pkg.go.dev/gorm.io/gorm#DB
	client *gorm.DB
	// sirupsen/logrus logger used in worker functions
	//
	// https://pkg.go.dev/github.com/sirupsen/logrus#Entry
	logger *logrus.Entry
	}

This engine contains no raw SQL queries for integrating with the workers table.

Instead, we leverage our DB library's (https://gorm.io/) agnostic abstraction for integrating with that table.

[cognifloyd]

I see that this moves from GetWorker to GetWorkerByHostname which is much better.

It also drops GetWorkerByAddress - should we re-add that?

[jbrockopp]

@cognifloyd GetWorkerByAddress was not used anywhere in the codebase 😅

When I discovered this during the refactor, I elected to not include it.

However, if we feel there is a good reason to keep it, I could certainly do so.