Ability to retain specialised pods for poolmanager functions (#2830)

- added retainPods flag to take in the number of specialized pods to retain
- add retainPods in both the create function and update function command
- modify crd keys to be typed instead of string
- keep track of function generation in case of update function operation
- add delete handler function to make sure specialized pods are deleted in case function is deleted

---------

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>
Signed-off-by: Pranoy Kundu <pranoy1998k@gmail.com>
Co-authored-by: Pranoy Kundu <pranoy1998k@gmail.com>

pkg/fission-cli/flag/flag.go

@@ -132,6 +132,7 @@ var (
 	FnOnceOnly              = Flag{Type: Bool, Name: flagkey.FnOnceOnly, Aliases: []string{"yolo"}, Usage: "Specifies if specialized pod will serve exactly one request in its lifetime"}
 	FnSubPath               = Flag{Type: String, Name: flagkey.FnSubPath, Usage: "Sub Path to check if function internally supports routing"}
 	FnLogAllPods            = Flag{Type: Bool, Name: flagkey.FnLogAllPods, Usage: "Get all pod's logs in the function."}
+	FnRetainPods            = Flag{Type: Int, Name: flagkey.FnRetainPods, Usage: "Number of pods to retain after pods specialization.", DefaultValue: 0}
 	// Termination Grace Period configurable at function creation/update only for container functions
 	FnTerminationGracePeriod = Flag{Type: Int64, Name: flagkey.FnGracePeriod, Usage: "Grace time (in seconds) for pod to perform connection draining before termination (only non-negative values considered)", DefaultValue: 360}
 

pkg/fission-cli/flag/key/key.go

@@ -86,6 +86,7 @@ const (
 	FnSubPath               = "subpath"
 	FnGracePeriod           = "graceperiod"
 	FnLogAllPods            = "all-pods"
+	FnRetainPods            = "retainpods"
 
 	HtName              = resourceName
 	HtMethod            = "method"