Install phpDocumentor and Doctum

Summary:
Require Graphviz and PlantUML for phpDocumentor.

Don't require any binding for GraphViz, it calls directly dot.

Ref T1718

Test Plan:
Generate documentation for Keruald Omnitools
both with phpDocumentor and Doctum.

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1718

Differential Revision: https://devcentral.nasqueron.org/D2662