fleetctl preview: Error message if license key is invalid

[rachaelshaw]

Goal

User story
As a user running fleetctl preview,
I want to see an error message if my license key is invalid
so that I can fix the issue & continue evaluating Fleet.

Objective

Original requests

• fleetctl preview: if license key invalid, then show error (instead of folks' first-time experience being that it hangs with no feedback) #22884

Context

• Product designer: @rachaelshaw

Changes

Product

• UI changes: TODO
• CLI (fleetctl) usage changes: TODO
• YAML changes: TODO
• REST API changes: TODO
• Fleet's agent (fleetd) changes: TODO
• Activity changes: TODO
• Permissions changes: TODO
• Changes to paid features or tiers: TODO
• Other reference documentation changes: TODO
• Once shipped, requester has been notified

Engineering

• Feature guide changes: TODO
• Database schema migrations: TODO
• Load testing: TODO

ℹ️  Please read this issue carefully and understand it. Pay special attention to UI wireframes, especially "dev notes".

QA

Risk assessment

• Requires load testing: TODO
• Risk level: Low / High TODO
• Risk description: TODO

Manual testing steps

1. Step 1
2. Step 2
3. Step 3

Testing notes

Confirmation

1. Engineer (@____): Added comment to user story confirming successful completion of QA.
2. QA (@____): Added comment to user story confirming successful completion of QA.