Update Licensing Model doc to include Mimir

Subtask tied to moving Mimir from Sandbox to Incubating status: big-bang/product/bbtoc!175 (merged)

Need to update https://repo1.dso.mil/big-bang/bigbang/-/blob/master/docs/understanding-bigbang/licensing-model.md#table-to-help-elaborate-on-nuances-of-application-licensing to include a row for Mimir.