Clean up unused azure vms or services

We still have running and no longer used vms (and maybe services). Let's investigate what really needs to run and stop what's not needed (and stop then destroy those):

|------------------+---------+------------+---------------------------------------------------------------|
| node             | status  | new status | note                                                          |
|------------------+---------+------------+---------------------------------------------------------------|
| cassandra[01-06] | stopped | dropped    | no longer required                                            |
| mirror-test      | running | dropped    | no longer required [in terraform manifest]                    |
| dbreplica0       | running | dropped    | softwareheritage db replication in azure (unused)             |
| dbreplica1       | running |            | replicated softwareheritage-indexer db (sole indexer db copy) |
| storage01        | running |            | required but some services can be stopped                     |
| storage02        | stopped | dropped    | no longer required                                            |
| ns0              | running |            | required: secondary azure dns                                 |
| vangogh          | running |            | required: vault server                                        |
| worker[01-13]    | running |            | indexer and cooker workers                                    |
| webapp0          | stopped | dropped    | associated dangling resources left-over                       |
|------------------+---------+------------+---------------------------------------------------------------|

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Migrated from T3903 (view on Phabricator)