Physical disks in the rack should have their slot number recorded.

Currently in the database we have a number of fields for a physical disk, but don't have
the slot number where the disk is located. This should be included.

root@[fd00:1122:3344:107::3]:32221/omicron> select * from physical_disk;                                                                                                                                                                                                                                                                                                                                                                              
                   id                  |         time_created          |         time_modified         | time_deleted | rcgen | vendor |    serial    |           model           | variant |               sled_id                                                                                                                                                                                                                                   
---------------------------------------+-------------------------------+-------------------------------+--------------+-------+--------+--------------+---------------------------+---------+---------------------------------------
  0162b5c1-8aa4-40ae-ad44-467545235f79 | 2023-08-30 18:57:22.773369+00 | 2023-09-12 20:50:09.967072+00 | NULL         |     1 | 1b96   | A079E3A6     | WUS4C6432DSP3X3           | u2      | 5f6720b8-8a31-45f8-8c94-8e699218f28b
  0177a6c7-f878-47b8-a0c1-8b8b382fe969 | 2023-08-30 18:57:24.253329+00 | 2023-09-12 21:06:23.133969+00 | NULL         |     1 | 1b96   | A084A607     | WUS4C6432DSP3X3           | u2      | db183874-65b5-4263-a1c1-ddb2737ae0e9
  0406b8ce-6813-49cf-b4de-39dc89b40c78 | 2023-08-30 18:57:24.324508+00 | 2023-09-12 20:46:55.420221+00 | NULL         |     1 | 1b96   | A084A6F6     | WUS4C6432DSP3X3           | u2      | b886b58a-1e3f-4be1-b9f2-0c2e66c6bc88
  0457777a-9017-4f7f-9ae7-62de62157161 | 2023-08-30 18:57:22.729825+00 | 2023-09-12 21:06:23.140654+00 | NULL         |     1 | 1b96   | A079E1A0     | WUS4C6432DSP3X3           | u2      | 5f6720b8-8a31-45f8-8c94-8e699218f28b

Start at the physical_disk table shown in the issue and locate its schema and the entry points that create or read physical-disk records. Add the requested slot number consistently, then verify that querying physical_disk exposes the new value; no specific files or tests are named in the issue.