Icinga Web Performance Data Graphs Graphite Backend

What's Changed

• Use placeholder in forms by @martialblog in https://github.com/NETWAYS/icingaweb2-module-perfdatagraphs-graphite/pull/9
• Fix config validation for Graphite by @martialblog in https://github.com/NETWAYS/icingaweb2-module-perfdatagraphs-graphite/pull/10

Full Changelog: https://github.com/NETWAYS/icingaweb2-module-perfdatagraphs-graphite/compare/v0.1.1...v0.1.2