You have not mentioned if you want it for the Edit/Live Preview mode, or for Reading mode, or for both.
Here is the code for both Edit (= CM5) and Reading mode:
.cm-s-obsidian, .markdown-preview-view {
text-align: justify;
hyphens: auto;
}
If, instead of Edit/CM5 you want Live Preview/CM6, you can replace .cm-s-obsidian by .markdown-source-view.mod-cm6.is-live-preview.
Having said that (last paragraph), it might not be sufficient (I have not checked), in which case you might also have to add the .cm-s-obsidian.