blueprint diffs: when something has changed, report all the fields that were compared

[davepacheco]

(This might be obviated by #7240.)

In #7299, something that threw me off (for kind of a while) was that the diff reported these changed rows but they looked identical:

# omdb nexus blueprints diff current 2e24acb1-21c8-469a-ace5-bec12f89a539
...

 MODIFIED SLEDS:

  sled 09301471-54be-465e-a674-45da58c0c59b (active):

...
    datasets generation 1 -> 2:
    -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
    dataset name                                                                                                   dataset uuid                           quota     reservation   compression
    -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
    oxp_13a7b934-412b-4ea5-8391-d52998c2c6fe/crucible                                                              36b554b7-d442-4c58-96fe-71f88d9145e6   none      none          off
    oxp_29f71bd8-8d07-44f9-a587-8dd6552d6b3d/crucible                                                              53b65adf-99c3-472b-849c-9385e61c7f80   none      none          off
    oxp_639dcdf6-d036-4e59-94d8-9a05706f2a6e/crucible                                                              ee41d385-8bc3-4932-971a-2f2b1b3461a1   none      none          off
    oxp_b5c23cec-84ac-4810-9077-3f960af72fcd/crucible                                                              ab04e945-3a16-4a33-8e8b-a87b7d51df6f   none      none          off
    oxp_b9dc2f06-bf04-463c-8ffe-79d8357d852b/crucible                                                              9f46899f-ee8c-46e1-b6a3-99f74974379f   none      none          off
*   oxp_13a7b934-412b-4ea5-8391-d52998c2c6fe/crypt/clickhouse                                                      ff1f90df-76b9-46a1-b2aa-c960db481817   none      none          off
*   oxp_13a7b934-412b-4ea5-8391-d52998c2c6fe/crypt/cockroachdb                                                     355ddd2b-b336-45c6-903f-ecdc99b26289   none      none          off
*   oxp_13a7b934-412b-4ea5-8391-d52998c2c6fe/crypt/debug                                                           50e80495-eb69-4716-8fa4-9f697b454498   100 GiB   none          gzip-9
*   oxp_13a7b934-412b-4ea5-8391-d52998c2c6fe/crypt/external_dns                                                    5c81c9ca-43b3-43a2-ae34-2b2d09544492   none      none          off
...

Should we say that if the tool reports some row having changed, then it should print out all of the fields that were compared so that the user can see what changed?

[davepacheco]

I ran into another case where a dataset is changed in the diff output but it's not clear why: when the dataset gets expunged (because it's associated with a zone that's expunged). The disposition goes from "in service" to "expunged".