Outline v0.64.0 requires valid COLLABORATION_URL

[luclu]

Since v0.64.0 Outline requires a valid COLLABORATION_URL (See SERVICES.md):

"We also introduced stricter validation of all environment variables to help with debugging and setup of the community edition, depending on your environment this may result in new errors or warnings being output upon server startup."

Currently this values is dictated by the chart's templating:

outline-helm-chart/templates/outline.yaml

Lines 32 to 33 in 7293f76

	- name: COLLABORATION_URL
	value: ""

Adding another ENV works, but is not clean.