Tracking issue: reqwest `default-tls` feature

Although no uses of reqwest within Omicron use the default-tls feature, because of the use of a workspace-hack crate all of our reqwest clients are using native-tls (thus OpenSSL) by default. I don't think we've ever written down our decision of whether to use native-tls or rustls but all of our Dropshot services use rustls (the default), and it is generally speaking our preference to have one TLS implementation, not two.

├── reqwest feature "__tls"
│   ├── reqwest feature "__rustls" (*)
│   └── reqwest feature "default-tls"
│       └── reqwest feature "default"
│           ├── crucible-agent-client v0.0.1 (https://github.com/oxidecomputer/crucible?rev=d2d8f8ad449df7e2befb7ee2723a442dd74b9b72#d2d8f8ad)
│           │   └── crucible-agent-client feature "default"
│           │       ├── nexus-test-utils v0.1.0 (/home/iliana/git/omicron/nexus/test-utils) (*)
│           │       ├── omicron-nexus v0.1.0 (/home/iliana/git/omicron/nexus) (*)
│           │       ├── omicron-omdb v0.1.0 (/home/iliana/git/omicron/dev-tools/omdb) (*)
│           │       └── omicron-sled-agent v0.1.0 (/home/iliana/git/omicron/sled-agent) (*)
│           ├── crucible-pantry-client v0.0.1 (https://github.com/oxidecomputer/crucible?rev=d2d8f8ad449df7e2befb7ee2723a442dd74b9b72#d2d8f8ad)
│           │   └── crucible-pantry-client feature "default"
│           │       └── omicron-nexus v0.1.0 (/home/iliana/git/omicron/nexus) (*)
│           ├── ddm-admin-client v0.1.0 (https://github.com/oxidecomputer/maghemite?rev=cb2b592e890ca9e93d8193e9765e2a62459d5fa8#cb2b592e) (*)
│           ├── libfalcon v0.1.0 (https://github.com/oxidecomputer/falcon?branch=main#f3fe0542) (*)
│           ├── lldpd-client v0.1.0 (https://github.com/oxidecomputer/lldp#ce952e61)
│           │   └── lldpd-client feature "default"
│           │       └── omicron-nexus v0.1.0 (/home/iliana/git/omicron/nexus) (*)
│           ├── mg-admin-client v0.1.0 (https://github.com/oxidecomputer/maghemite?rev=cb2b592e890ca9e93d8193e9765e2a62459d5fa8#cb2b592e) (*)
│           └── omicron-workspace-hack v0.1.0 (/home/iliana/git/omicron/workspace-hack) (*)

This issue tracks dropping the default-tls feature (at least by default) from:

• Crucible (waiting for Maghemite)
• Maghemite: https://github.com/oxidecomputer/maghemite/pull/437
• FALCON: https://github.com/oxidecomputer/falcon/pull/105
• lldp: https://github.com/oxidecomputer/lldp/pull/19

And then:

• Set up cargo-deny in CI and deny native-tls to prevent this accidentally happening again

Start with the workspace-hack dependency tree and the linked Crucible, Maghemite, FALCON, and lldp changes to identify which upstream features still enable reqwest default-tls. Then review how cargo-deny would be added to CI. Done means the remaining upstream checkboxes are resolved and CI denies native-tls from being reintroduced.