tarantool.config: add `wait_status` helper

Related dev. issue(s): https://github.com/tarantool/tarantool/pull/12439

Product: Tarantool
Since: 3.7
Root document: https://www.tarantool.io/en/doc/latest/reference/reference_lua/config/
SME: @georgiy-belyanin, @mandesero

Details

Introduce a new helper function config:wait_status() that allows waiting for one of the specified configuration statuses.

config API

config:wait_status(statuses[, timeout])

Wait until the instance reaches one of the specified configuration statuses.

The call is blocking: it suspends the current fiber until the instance transitions to any of the given statuses. If no timeout is specified, the function waits indefinitely.

Parameters:

• statuses (table) - a list of statuses to wait for
• timeout (number) - maximum time to wait (in seconds); if not specified, waits indefinitely

Return: the reached status

Example:

local function apply(cfg)
    fiber.create(function()
        -- Wait until status changes to one of the expected values.
        -- If the status never reaches 'check_errors', this fiber will block indefinitely.
        local status = config:wait_status({'check_errors'})

        if status == 'check_errors' then
            -- Handle configuration errors
        end
    end)

    -- Continue applying configuration
end

Start with the root document at reference/reference_lua/config/ and review related development pull request #12439 for the implementation context. Document the config:wait_status() API, including statuses, optional timeout, blocking behavior, return value, and the example shown here. Done means the helper is accurately represented in the configuration reference and the documentation build passes.