Introduce a first-class DirectorProperty concept that extends the existing
data-fields model with rich, structured variable types. Custom variables can
now be defined globally under a new "Custom Variables" section and assigned
to Icinga objects (hosts, services, commands, etc.).
Supported types: string, number, boolean, fixed-array, dynamic-array,
datalist-strict, datalist-non-strict, fixed-dictionary, and
dynamic-dictionary (one level of nesting allowed).
Key changes:
- DirectorProperty object with CRUD, inheritance, and apply-for rule support
- New form elements: Dictionary, DictionaryItem, NestedDictionary,
NestedDictionaryItem, ArrayElement, IplBoolean
- CustomvarController for managing global property definitions
- VariablesController for per-object variable assignment
- BasketSnapshotCustomVariableResolver for basket import/export of properties
- REST API: IcingaObjectHandler extended to expose and accept structured vars
- IcingaConfigHelper: renders dictionaries/arrays to valid Icinga 2 DSL
- CustomVarRenderer updated for icingadb hook display
- DB migration upgrade_192.sql: new director_property and related tables
- CLI: MigrateCommand for migrating legacy vars to properties;
HostsCommand for bulk host custom variable management
