feat: add support for schedules

[jbrockopp]

xref: go-vela/community#538

Part of go-vela/community#772

This adds a new schedule event type which will be used in go-vela/server.

This also adds some test cases for ruleset in the pipeline and yaml packages.

Additionally, this adds a new Schedule{} type to the github.com/go-vela/types/database package:

types/database/schedule.go

Lines 29 to 41 in cb989d1

	// Schedule is the database representation of a schedule for a repo.
	type Schedule struct {
	ID sql.NullInt64 `sql:"id"`
	RepoID sql.NullInt64 `sql:"repo_id"`
	Active sql.NullBool `sql:"active"`
	Name sql.NullString `sql:"name"`
	Entry sql.NullString `sql:"entry"`
	CreatedAt sql.NullInt64 `sql:"created_at"`
	CreatedBy sql.NullString `sql:"created_by"`
	UpdatedAt sql.NullInt64 `sql:"updated_at"`
	UpdatedBy sql.NullString `sql:"updated_by"`
	ScheduledAt sql.NullInt64 `sql:"scheduled_at"`
	}

And adds a new Schedule{} type to the github.com/go-vela/types/library package:

types/library/schedule.go

Lines 11 to 25 in cb989d1

	// Schedule is the API representation of a schedule for a repo.
	//
	// swagger:model Schedule
	type Schedule struct {
	ID *int64 `json:"id,omitempty"`
	RepoID *int64 `json:"repo_id,omitempty"`
	Active *bool `json:"active,omitempty"`
	Name *string `json:"name,omitempty"`
	Entry *string `json:"entry,omitempty"`
	CreatedAt *int64 `json:"created_at,omitempty"`
	CreatedBy *string `json:"created_by,omitempty"`
	UpdatedAt *int64 `json:"updated_at,omitempty"`
	UpdatedBy *string `json:"updated_by,omitempty"`
	ScheduledAt *int64 `json:"scheduled_at,omitempty"`
	}

These will be used in the go-vela/server to create a new schedules table in the database.

[codecov]

Codecov Report

Merging #289 (cb989d1) into main (1203118) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #289      +/-   ##
==========================================
+ Coverage   96.90%   97.00%   +0.10%     
==========================================
  Files          57       59       +2     
  Lines        6329     6545     +216     
==========================================
+ Hits         6133     6349     +216     
  Misses        145      145              
  Partials       51       51              

Impacted Files	Coverage Δ
pipeline/ruleset.go	100.00% <ø> (ø)
yaml/ruleset.go	100.00% <ø> (ø)
database/schedule.go	100.00% <100.00%> (ø)
library/schedule.go	100.00% <100.00%> (ø)

[ecrupper]

This meant to still be in draft? LGTM