Database configuration backend

[nilmerg]

At the moment we store most of our configuration on disk in INI files. While this allows easy editing it requires duplicating configuration in a clustered environment.

Subtasks:

• Enforce as default backend (Enforce database as configuration backend #4135)
• Dashboards (Store dashboards in database instead of local files (useful for HA environments) #1704, Enhanced Dashboards #3809, Feature: Enhanced Dashboards #4323)
• Navigation ([dev.icinga.com #10877] Store menu entries in database instead of local files #2209)

Enforce as default backend

At the moment we provide support for INI files and a database as configuration backend. With the release of v2.9.0 we are going to deprecate INI files and enforce a database as configuration backend for new installations.

This requires the following changes:

• The setup wizard does not allow the user to choose the backend type, it enforces the setup of the database as backend.
• The general configuration of Icinga Web 2 also does not provide a way to configure the configuration backend type. It only allows to choose a specific database resource to use.
• INI files as preferences backend are still supported, but only by configuration. If this backend type is detected, a warning should appear in the log telling the user that this is deprecated and will be removed with version 2.10.
• Code which needs access to the configuration backend should make use of the trait Icinga\Common\Database which utilizes the resource configured in the general configuration.

Development Hints

If the setup module is enabled, the setup is accessible by visiting /icingaweb2/setup. It can be started by entering a token that needs to be generated on the server. (Use icingacli setup token create in the web container)

• WebWizard::getRequirements() defines what is necessary to start the setup. Currently the database adapters for MySQL and PostgreSQL are both optional. This needs to change so that at least either of the two must be available.
• Throughout the following steps the wizard must assume database as configuration backend by default.
• WebWizard::getNewPage() controls whether DbResourcePage is shown in case the database is not already set-up due to the authentication config.
• Class GeneralConfigPage is used to let the user configure the general configuration of Icinga Web 2. This includes choosing which backend to use to store user preferences. This option needs to be removed so that the user can't choose the backend type anymore. This also requires changes in WebWizard::setupPage() as it's accessing the page's element.
• Further on, anytime Icinga Web 2 accesses a user's preferences it should assume that a database is used as backend by default. Check where PreferencesStore::create() is utilized to get an idea how to accomplish that. Remember to log a warning for INI backends.
• Class GeneralConfigForm needs to also show a warning if INI is detected as configuration backend type. To accomplish that implement method onRequest() in this class, inspect the configuration object and show a warning with $this->warning().