Add runner rotate ability to CLI

This change adds a new "generation" field to pools, scalesets and
runners. The generation field is inherited by runners from scale sets
or pools at the time of creation.

The generation field on scalesets and pools is incremented when the
pool or scale set is updated in a way that might influence how runners
are created (flavor, image, specs, runner groups, etc).

Using this new field, we can determine if existing runners have diverged
from the settings of the pool/scale set that spawned them.

In the CLI we now have a new set of commands available for both
pools and scalesets that lists runners, with an optional --outdated
flag and a new "rotate" flag that removes all idle runners. Optionally
the --outdated flag can be passed to the rotate command to only remove
outdated runners.

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

database/sql/models.go

@@ -121,6 +121,14 @@ type Pool struct {
 	GitHubRunnerGroup string
 	EnableShell       bool
 
+	// Generation holds the numeric generation of the pool. This number
+	// will be incremented, every time certain settings of the pool, which
+	// may influence how runners are created (flavor, specs, image) are changed.
+	// When a runner is created, this generation will be copied to the runners as
+	// well. That way if some settings diverge, we can target those runners
+	// to be recreated.
+	Generation uint64
+
 	RepoID     *uuid.UUID `gorm:"index"`
 	Repository Repository `gorm:"foreignKey:RepoID;"`
 
@@ -178,6 +186,13 @@ type ScaleSet struct {
 	ExtraSpecs  datatypes.JSON
 	EnableShell bool
 
+	// Generation is the scaleset generation at the time of creating this instance.
+	// This field is to track a divergence between when the instance was created
+	// and the settings currently set on a scaleset. We can then use this field to know
+	// if the instance is out of date with the scaleset, allowing us to remove it if we
+	// need to.
+	Generation uint64
+
 	RepoID     *uuid.UUID `gorm:"index"`
 	Repository Repository `gorm:"foreignKey:RepoID;"`
 
@@ -336,6 +351,12 @@ type Instance struct {
 	GitHubRunnerGroup string
 	AditionalLabels   datatypes.JSON
 	Capabilities      datatypes.JSON
+	// Generation is the pool generation at the time of creating this instance.
+	// This field is to track a divergence between when the instance was created
+	// and the settings currently set on a pool. We can then use this field to know
+	// if the instance is out of date with the pool, allowing us to remove it if we
+	// need to.
+	Generation uint64
 
 	PoolID *uuid.UUID
 	Pool   Pool `gorm:"foreignKey:PoolID"`