Make it possible to disable the auto-refresh "Custom interval" option

[fhyy]

Version 4.1.0 added an auto-refresh interval option "Custom interval" (see #24449) which is useful in many situations, but sometimes one might want to remove this option.

A dashboard containing never-changing data does not need a refresh at all. In this case even the "Set auto-refresh interval" menu option could be disabled completely.

A dashboard of many charts - performing some expensive queries - needs to put limit on the user by only allowing a set of predefined intervals such as "1 hour", "6 hours", etc. This can be done by overriding the option DASHBOARD_AUTO_REFRESH_INTERVALS

DASHBOARD_AUTO_REFRESH_INTERVALS = [
    [0, "Don't refresh"],
    [3600, "1 hour"],
    [21600, "6 hours"],
    [43200, "12 hours"],
    [86400, "24 hours"],
]

However, the option "Custom interval" is always present and cannot be removed as far as I know:

    refresh_options.push({ value: -1, label: t('Custom interval') });
    refresh_options.push(
      ...refreshIntervalOptions.map(option => ({
        value: option[0],
        label: t(option[1]),
      })),
    );

This means that the user is always able to set a refresh interval of 1 second ⚠️

Suggestion

Add the option [-1, "Custom interval"] to the default config and remove the code that always pushes it to the list:

DASHBOARD_AUTO_REFRESH_INTERVALS = [
    [-1, "Custom interval"],
    [0, "Don't refresh"],
    [10, "10 seconds"],
    [30, "30 seconds"],
    [60, "1 minute"],
    [300, "5 minutes"],
    [1800, "30 minutes"],
    [3600, "1 hour"],
    [21600, "6 hours"],
    [43200, "12 hours"],
    [86400, "24 hours"],
]

    # refresh_options.push({ value: -1, label: t('Custom interval') });
    refresh_options.push(
      ...refreshIntervalOptions.map(option => ({
        value: option[0],
        label: t(option[1]),
      })),
    );

This makes it possible to remove the option when overriding the config.

Additionally the "Set auto-refresh interval" menu option could be hidden if the DASHBOARD_AUTO_REFRESH_INTERVALS list is empty.