describes available statuses

This PR is a replication of a PR by @ulferts  against **[opf/op-api-v3-documentation](https://github.com/opf/op-api-v3-documentation)**.

Original PR: https://github.com/opf/op-api-v3-documentation/pull/7

Note that this PR is probably **not safely mergable** as of now.

Original Description
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*No description provided.*