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/cmd/function/create.go

@@ -104,6 +104,7 @@ func (opts *CreateSubCommand) complete(input cli.Input) error {
 	}
 
 	requestsPerPod := input.Int(flagkey.FnRequestsPerPod)
+	retainPods := input.Int(flagkey.FnRetainPods)
 
 	fnOnceOnly := input.Bool(flagkey.FnOnceOnly)
 
@@ -306,6 +307,7 @@ func (opts *CreateSubCommand) complete(input cli.Input) error {
 			IdleTimeout:     &fnIdleTimeout,
 			Concurrency:     fnConcurrency,
 			RequestsPerPod:  requestsPerPod,
+			RetainPods:      retainPods,
 			OnceOnly:        fnOnceOnly,
 		},
 	}