Measure used disk storage

[fm3]

webKnossos now measures the storage used by the datasets of the organizations.
New config options datastore.reportUsedStorage.enabled and webKnossos.fetchUsedStorage.interval.
Note that the organization is re-scanned regularly, but dataset upload + delete trigger a refresh of said dataset directly.
Datastores report that they have reportUsedStorage.enabled to webKnossos, which then stores that info in the postgres datastores table.
Load distribution strategy assumes that measuring a single organization isn’t that huge an operation (optimized for multi-orga setup).

Steps to test:

• turn on storage reporting as described above
• start up, after initial delay, the organization api request should include used storage
• test with multiple organizations that the load distribution logic works

Issues:

• fixes Calculate storage use #6614

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• Updated (unreleased) changelog
• Updated (unreleased) migration guide if applicable
• Needs datastore update after deployment
• Ready for review

[jstriebel]

Thanks for the clarifications, LGTM 👍

[fm3]

@philippotto could you have a quick look at the latest commit cd80b77 ? I adapted the front-end to use the new measured value

[philippotto]

@philippotto could you have a quick look at the latest commit cd80b77 ? I adapted the front-end to use the new measured value

Looks good to me 👍