Refactor cli command initialisation and error reporting

[DavidS-ovm]

This unifies all commands to use shared setup/login/error reporting facilities and provide usage info when flag validation fails.

Examples for flagErrors:

vscode ➜ /workspace/cli (dev) $ time go run main.go request load --snapshot-uuid foo
Failed to parse UUID 'foo': invalid UUID length: 3

Usage:
  overmind request load [flags]

Flags:
      --app string             The overmind instance to connect to. (default "https://app.overmind.tech")
[...]

vscode ➜ /workspace/cli (dev) $ time go run main.go request load --snapshot foo
unknown flag: --snapshot

Usage:
  overmind request load [flags]

Flags:
      --app string             The overmind instance to connect to. (default "https://app.overmind.tech")
[...]

Example for loggedError:

vscode ➜ /workspace/cli (dev) $ time go run main.go request query --query foo
ERRO Failed to connect to overmind API             error="failed to WebSocket dial: expected handshake response status code 101 but got 200" gateway-url="https://api.df.overmind-demo.com/api/gateway"

[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ *errors.errorString: processPlanCmd: risks errored github.com/overmindtech/cli/cmd in (*cmdModel).... View Issue

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