update reconfigurator-cli, blueprint show, blueprint diff for SP updates

[davepacheco]

This adds support to reconfigurator-cli for configuring SP updates in blueprints. As part of this:

• the blueprint builder supports changes to pending_mgs_updates
• blueprint diff now shows changes to pending_mgs_updates
• we now have tests for basic manipulation of this structure (through the reconfigurator-cli tests)

(follows #7976)

[davepacheco]

Don't be put off by the size of the diff. It's almost all in the expected output file of the new reconfigurator-cli test:

$ git diff --stat main
 dev-tools/reconfigurator-cli/src/lib.rs                              |  103 ++-
 dev-tools/reconfigurator-cli/tests/input/cmds-set-mgs-updates.txt    |   42 +
 dev-tools/reconfigurator-cli/tests/output/cmd-set-mgs-updates-stderr |    3 +
 dev-tools/reconfigurator-cli/tests/output/cmd-set-mgs-updates-stdout | 2835 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 dev-tools/reconfigurator-cli/tests/output/cmd-set-zone-images-stdout |   12 +-
 dev-tools/reconfigurator-cli/tests/test_basic.rs                     |   17 +
 nexus/reconfigurator/planning/src/blueprint_builder/builder.rs       |   25 +-
 nexus/types/src/deployment.rs                                        |   24 +-
 nexus/types/src/deployment/blueprint_diff.rs                         |  131 ++-
 nexus/types/src/deployment/blueprint_display.rs                      |   14 +-
 10 files changed, 3175 insertions(+), 31 deletions(-)

Ignoring that file, it's only +340/-31.

[andrewjstone]

Looks good! So great to see this coming together.