Public alerts API

Dev. issue: https://github.com/tarantool/tarantool/issues/10873

Product: Tarantool
Since: 3.3.0
Root document: https://www.tarantool.io/en/doc/latest/reference/reference_lua/config/
SME: @ grafin

Details

Users can now raise their own alerts (similar to the alerts raised by
the config module).

New available methods:

• config:new_alerts_namespace(alerts_namespace_name) - creates a new
  alerts namespaces and returns it. alerts_namespace_name must be a
  string and can not contain a colon (":").
• alerts_namespace:add(alert) - raises new alert of type warning.
  alert must be a table. alert.message is logged and the alert will
  be shown in box.info.config.alerts.
• alerts_namespace:set(key, alert) - raises new alert of type warning,
  or replaces an existing, raised with the same 'key' in the namespace.
  alert must be a table. alert.message is logged and the alert will
  be shown in box.info.config.alerts. key must be a string and can
  not contain a colon (":").
• alerts_namespace:unset(key) - discards the alert with the
  corresponding 'key' in the namespace. key must be a
  string and can not contain a colon (":"). If an alert with the
  corresponding key does not exist in the namespace, does nothing.
• alerts_namespace:clear() - discards all alerts from the namespace,
  removing them from box.info.config.alerts.

Alerts namespaces with the same name will point to the same alerts
namespace. During configuration update all alerts from namespaces are
removed from box.info.config.alerts.

The alert.type is forced to be "warn", anything except "warn" or
nil is considered an error.

Any keys in alert which start with an underscore will be ignored.

Example usage:

local config = require('config')

-- Create a new alerts namespace 'my_alerts'.
local alerts = config:new_alerts_namespace('my_alerts')

-- Raise a new alert.
alerts:add({
    message = 'Test alert',
    my_field = 'my_value',
})

-- Raise a new alert with a key.
alerts:set("my_alert", {
    message = 'Test alert',
    my_field = 'my_value',
})

-- Update an existing alert with a key.
alerts:set("my_alert", {
    message = 'Test alert',
    my_field = 'my_value',
})

-- Discard an existing alert with a key.
alerts:unset("my_alert")

-- Clear all alerts in the alerts namespace 'my_alerts'
alerts:clear()

Requested by @grafin in https://github.com/tarantool/tarantool/commit/469134625b832244398a1e9b55d08c27648a6990.

Start with the linked root document for the Lua config API and review its existing alert documentation. Add the public namespace creation and alert lifecycle methods described in the issue, including validation and cleanup behavior, then verify the examples and API descriptions cover the stated acceptance details.