GEP: Support ClientIp based session persistence

[arihantg]

What would you like to be added:
SessionPersistence should support client IP address mode. With this persistence method client will stick to the same BE for the configurable duration of time (Absolutetimeout). User should have an option to set IPMask as well which can be applied on client ip to persist clients from a subnet to stick to the same BE.

2 New fields are needed

1. IPMask should be added in SessionPersistence struct,
2. ClientIPBasedSessionPersistence should be a new SessionPersistenceType .

type SessionPersistence struct {
	// SessionName defines the name of the persistent session token
	// which may be reflected in the cookie or the header. Users
	// should avoid reusing session names to prevent unintended
	// consequences, such as rejection or unpredictable behavior.
	//
	// Support: Implementation-specific
	//
	// +optional
	// +kubebuilder:validation:MaxLength=128
	SessionName *string `json:"sessionName,omitempty"`

        // IPMask defines the IP mask to be applied on client this may be
	// used to persist clients from a same subnet to stick to same session
	//
	// Support: Implementation-specific
	//
	// +optional
	IPMask *string `json:"ipMask,omitempty"`

}

type SessionPersistenceType string

const (
    // CookieBasedSessionPersistence specifies cookie-based session
    // persistence.
    //
    // Support: Core
    CookieBasedSessionPersistence   SessionPersistenceType = "Cookie"

    // HeaderBasedSessionPersistence specifies header-based session
    // persistence.
    //
    // Support: Extended
    HeaderBasedSessionPersistence   SessionPersistenceType = "Header"

    // ClientIPBasedSessionPersistence specifies Client IP based session
    // persistence.
    //
    // Support: Implementation-specific
    ClientIPBasedSessionPersistence   SessionPersistenceType = "ClientIP"
)

Why this is needed:
This is needed to support client Ip Persistence in centralised way across gateway implementations.

[shaneutt]

This feature has been accepted for the v1.4.0 release. Please see this announcement for more details, and for the timing expectations for transitions. Note that if the timeline can not be met, there is a risk that this feature may unfortunately need to be dropped from the release. If you have any questions, concerns, or are in need of support please reach out to the maintainers so we can assist you!

Note: This feature only currently has one reviewer assigned (@sunjayBhatia) to help ensure things move along smoothly, we recommend you reach out and get a commitment from at least one more reviewer to support the iterations on this feature.

[shaneutt]

@arihantg as you start work on this, please make sure you review the existing https://gateway-api.sigs.k8s.io/geps/gep-1619/. Your GEP will need to reference 1619, and particularly call out any interactions (or problems) between the two.

[mikemorris]

Another relevant note is that in the Gateway API v1.3 release, SessionPersistence moved from BackendLBPolicy to the XBackendTrafficPolicy resource alongside the newly-introduced retry budgets, in an attempt to consolidate functionality on fewer policy CRDs rather that encouraging proliferation of many distinct CRDs for various policies across a similar scope.