feat(docs): unify response schema for the GetSessions endpoint

[kaua-alves-queiros]

feat(docs): unify response schema for the GetSessions endpoint

• Adopted a single predictable schema (GetSessionsResponse) for all endpoint responses
• Overrides the middleware's default documentation (403), ensuring consistent return types
• Added 404 response for when no sessions are found
• Added a success message in the response object
• Updates swagger documentation for 200, 404, 403, and 500 using the same schema
• Improves SDK consistency (nswag now generates only one response class)

autogenerated GetSessionsResponse in c# example

[System.CodeDom.Compiler.GeneratedCode("NJsonSchema", "14.5.0.0 (NJsonSchema v11.4.0.0 (Newtonsoft.Json v13.0.0.0))")]
    public partial class GetSessionsResponse
    {

        [System.Text.Json.Serialization.JsonPropertyName("success")]
        public bool Success { get; set; }

        [System.Text.Json.Serialization.JsonPropertyName("result")]
        public System.Collections.Generic.ICollection<string> Result { get; set; }

        [System.Text.Json.Serialization.JsonPropertyName("message")]
        public string Message { get; set; }

        private System.Collections.Generic.IDictionary<string, object> _additionalProperties;

        [System.Text.Json.Serialization.JsonExtensionData]
        public System.Collections.Generic.IDictionary<string, object> AdditionalProperties
        {
            get { return _additionalProperties ?? (_additionalProperties = new System.Collections.Generic.Dictionary<string, object>()); }
            set { _additionalProperties = value; }
        }

    }

[avoylenko]

Thank you for your contribution. The PR adds a breaking change to the endpoint and I want always be compatible with older integrations.