api: add the buffer limit knob to the cluster

[ShyunnY]

What type of PR is this?

api: add the buffer limit knob to the cluster

What this PR does / why we need it:

This PR aims to define the configuration structure of the per_connection_buffer_limit_bytes feature knob

Which issue(s) this PR fixes:

Related issues #3278

[ShyunnY]

/retest

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.42%. Comparing base (c30d09f) to head (cf605ab).
Report is 34 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3390      +/-   ##
==========================================
+ Coverage   67.11%   67.42%   +0.30%     
==========================================
  Files         164      166       +2     
  Lines       23818    19184    -4634     
==========================================
- Hits        15986    12935    -3051     
+ Misses       6912     5320    -1592     
- Partials      920      929       +9     

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[ShyunnY]

By the way, when Connection exists in both CTP and BTP, we can abstract them both into api/v1alpha1/connection_types.go (only a small refactoring code is required).

The current connection_types.go only defines about CTP:

gateway/api/v1alpha1/connection_types.go

Lines 14 to 26 in 8206e11

	type Connection struct {
	// ConnectionLimit defines limits related to connections
	//
	// +optional
	ConnectionLimit *ConnectionLimit `json:"connectionLimit,omitempty"`
	// BufferLimit provides configuration for the maximum buffer size in bytes for each incoming connection.
	// For example, 20Mi, 1Gi, 256Ki etc.
	// Note that when the suffix is not provided, the value is interpreted as bytes.
	// Default: 32768 bytes.
	//
	// +kubebuilder:validation:XValidation:rule="type(self) == string ? self.matches(r\"^[1-9]+[0-9]*([EPTGMK]i|[EPTGMk])?$\") : type(self) == int",message="bufferLimit must be of the format \"^[1-9]+[0-9]*([EPTGMK]i|[EPTGMk])?$\""
	// +optional
	BufferLimit *resource.Quantity `json:"bufferLimit,omitempty"`

Can we structure it like this?

type struct BackendTrafficPolicyConnection {
  ...
}

type struct ClientTrafficPolicyConnection {
  ...
}

[shawnh2]

prefer BackendConnection and ClientConnection

[ShyunnY]

wow, this looks great, I vote!
In this PR we will focus on the design of the bufferLimit API, and I will open an additional PR to solve the reconstruction problem in the future.
@shawnh2

[arkodg]

LGTM thanks !

lets track the connection refactor with a separate GH issue

[zirain]

/retest