[MM-61756] Attribute Based Access Control - Phase 1 (#30785)

Attribute Based Access Control - Base
* MM-63662

* MM-63919

* MM-63954

* MM-63955 

* MM-63425

* MM-63426

* MM-63458

* MM-63459

* MM-63603

* MM-63845

* MM-64146

* MM-64199

* MM-64201

* MM-64233

* MM-64247

* MM-64268

---------

Co-authored-by: Harshil Sharma <harshilsharma63@gmail.com>
Co-authored-by: Pablo Andrés Vélez Vidal <pablovv2012@gmail.com>
Co-authored-by: abhijit-singh <abhijitsingh0702@gmail.com>
Co-authored-by: Harrison Healey <harrisonmhealey@gmail.com>

server/public/model/cel.go

@@ -0,0 +1,30 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+// ValueType indicates whether a value is a literal or another attribute.
+type ValueType int
+
+const (
+	LiteralValue ValueType = iota
+	AttrValue
+)
+
+// Condition represents a single logical condition (e.g., user.attributes.Team == "Engineering").
+type Condition struct {
+	// Left-hand side attribute selector (e.g., "user.attributes.Team").
+	Attribute string `json:"attribute"`
+	// The comparison operator.
+	Operator string `json:"operator"`
+	// Right-hand side value(s). Can be a single value or a slice for 'in'.
+	Value any `json:"value"`
+	// Type of the Value (LiteralValue or AttributeValue). Needed for comparisons like user.attr1 == user.attr2.
+	ValueType ValueType `json:"value_type"`
+}
+
+// VisualExpression represents a series of conditions combined with logical AND.
+type VisualExpression struct {
+	// Conditions is a list of individual conditions that will be ANDed together.
+	Conditions []Condition `json:"conditions"`
+}