Make the Nexus external API versioned

[sunshowers]

This is a tracking issue for making the Oxide external API versioned.

• support extra validation for versioned APIs dropshot-api-manager#25
• add ClientSpecifiesVersionInHeader::on_missing dropshot#1475
• Wait for a new Dropshot release
• Make the external API versioned (with api-version header being optional)
• Add api-version header to TypeScript client Pass api-version header oxide.ts#311
• Add api-version header to Go client: Support Nexus API version header oxide.go#343
• Add a way to communicate to the console that it should refresh itself