This adds a small CLI tool for developers to use when working with the
DB locally. It provides two functions:
1. Explicitly migrate the DB (which is normally only done when the
   workflow controller starts) to help test migrations:

     ```
     $ go run ./hack/db migrate
     INFO[0000] Migrating database schema                     clusterName=default dbType=postgres
     ```
2. Insert randomly-generated archived workflows into the DB, which is
   intended to help test query performance (e.g.
   argoproj#13601)

    ```
    $ time go run ./hack/db/main.go fake-archived-workflows --rows 100000
    Using seed 2600415997737113470
    Clusters: [cx5j6rrzm5vnkfqqr4d]
    Namespaces: [bs98pxsfhs9z v95848 hq76xbj4kq7vrdp49vm ghzj6vcrth 262wb8w2b8v2wd2p2p9]
    Inserted 100000 rows

    real    17m56.554s
    user    1m53.833s
    sys     0m43.581s
    ```

  This is obviously not as efficient as it could be, but it's only
  intended to be run on an adhoc basis when manually testing query
  performance. To make it fast, we'd probably have to switch to direct
  SQL inserts, which would couple this script to the logic in
  `persist/sqldb/workflow_archive.go`.

Signed-off-by: Mason Malone <[email protected]>

Signed-off-by: Mason Malone <[email protected]>

Signed-off-by: Mason Malone <[email protected]>

Signed-off-by: Mason Malone <[email protected]>

Signed-off-by: Mason Malone <[email protected]>

Signed-off-by: Mason Malone <[email protected]>

Signed-off-by: Mason Malone <[email protected]>

Signed-off-by: Mason Malone <[email protected]>