How can I add this heist to the HQ Contracts?

You need to add the following code under Config["HQ"]["Contracts"] in bd-computer/shared/config.hq.lua

shared/config.hq.lua
    ["Maze Bank Robbery"] = {
        name = "Maze Bank Robbery",
        category = "mazebank",
        info = {
            ["Expected Loot"] = {
                "??? UNK",
            },
            ["Requirments"] = {
                "??? UNK",
            },
        },
        image = "mazebank",
        price = 0,
        eventInfo = {
            name = "bd-heists:server:mazebank:start-job",
            type = "server",
            parameters = {},
        },
        minMembers = 6,
        maxMembers = 6,
 
        -- Expiration time is the time (in Minutes) you have to complete the contract from the moment it is reset/generated.
        expirationTime = 120, -- 20 minutes
 
        -- Reset time is the time (in Minutes) the contract will be unavailable for after it has expired/has been completed.
        -- For example if you complete the contract in 10 minutes and the reset time is 5 minutes, the contract will be unavailable for 5 minutes.
        -- Othewise if you don't complete the contract in 20 minutes and it expires, the contract will be unavailable for 5 minutes again.
        -- In other words exact reset time depends on when the contract was completed or expired.
        resetTime = 60, -- 5 minutes
 
        -- Functions
        canPurchase = function()
            return true
        end,
 
        canJoin = function()
            return true
        end,
 
        canStart = function()
            return true
        end,
    },