Add URL query for show all (branch) labels

[jameshadfield]

Tested manually & via /narratives/test/simultaneous-tree-updates

Closes #1573

[jameshadfield]

I've not added this to the dataset defaults (of the dataset JSON) because there's currently not an obvious place to put it. We would want it to be settable per-branch-label, so something like:

display_defaults: {
  branch_label: "aa", // already exists
  show_all_branch_labels: ["clade"], // one option, but locks us into "all"
  show_branch_labels: {clade: "all"} // keeps the door option to future options?
}

(There's also the related-but-separate desire to be able to set branch label titles.)

[jameshadfield]

The review-app appears to have been build ("-----> Launching... Released v5. https://auspice-feat-branch-lab-hdcfc5.herokuapp.com/ deployed to Heroku") however I see the following when loading that URL. I don't think this 🐛 is the fault of this PR however

[joverlee521]

Huh, the review app works for me now. There must have been something weird on Heroku's side.
(EDIT: I spoke too soon. The splash page loads now, but I still can't access individual datasets)
(EDIT2: After hard refreshing the page 5 times, the dataset loads now 😅 )

[joverlee521]

LGTM!

I pushed up commits to update the docs for URL params.

[jameshadfield]

Thanks @joverlee521!