feat(kv): support setting key/value pairs

[kate-goldenring]

Adds spin cloud key-value set command:

• Set kv pair with store as identifier spin cloud key-value set --store "foo"
• With link identifier spin cloud key-value set --label "foo" --app "myapp"
  Comparable to spin cloud sqlite execute command

The cloud API does not yet expose delete and list pairs endpoints, but once it does, I'll add them

[rylev]

Looks good - I think this would also benefit from some general refactoring, but that should be done after this is merged.

[rylev]

I'm not sure if Clap is smart enough to show the user that if they don't set this they have to set the app/label. If not, can we document that?

[kate-goldenring]

I made some small adjustments (some conflicts withs), and it detects and tells the user when they have miscombined the flags. For example:

Kates-MacBook-Pro :: ~/Programs/cloud-plugin 2 » cargo run -- kv set --app a          
    Finished dev [unoptimized + debuginfo] target(s) in 0.16s
     Running `target/debug/cloud-plugin kv set --app a`
error: The following required arguments were not provided:
    --label <LABEL>

USAGE:

And:

Kates-MacBook-Pro :: ~/Programs/cloud-plugin 2 » cargo run -- kv set --store s --app a 
    Finished dev [unoptimized + debuginfo] target(s) in 0.42s
     Running `target/debug/cloud-plugin kv set --store s --app a`
error: The argument '--store <STORE>' cannot be used with '--app <APP>'

USAGE:
    spin cloud key-value set --store <STORE>

For more information try --help