Zabbix

A.FGI..PS. [ZBXNEXT-1726] add support for optional Host Metadata to active agent for auto-registration

This commit introduces new optional host attributes HostMetadata and
HostMetadataItem that will help to differentiate hosts at host
auto-registration. The attributes are specified in Zabbix agent
configuration file.

If both HostMetadata and HostMetadataItem are defined HostMetadata
will be used.

Host metadata is limited to 255 utf-8 characters. Non-utf-8 characters
are not allowed, in this case host metadata will be ignored.

This commit also adds utf-8 check to all configuration parameter
values.

A new macro {HOST.METADATA} can be used in notifications and remote
commands.

In the frontend a new condition "Host metadata" was added in
configuration of action for auto-registration.

This commit changes database schema.