Adjust wording pricing change notification

[jankeromnes]

Is your feature request related to a problem? Please describe

In #15092, we've introduced two notifications (in /plans and /teams once UBP is enabled) that have this text:

Your account has been enabled for usage-based billing. Discover faster workspace classes and only pay for what you actually use. [Learn more]

The old monthly plans are deprecated and will be cancelled by End of March 2023.

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However, this text has a few issues:

1. Too verbose, or uses unnecessary empty space.
2. Focus on the personal account, not team plans or team billing.
3. Sounds like the user has been part of a closed beta list and not accessing a GA feature on Gitpod.io.
4. Voice and tone is not direct, using terms like discover.
5. Lack of clear action. Do we want to provide an action for users or nudge to perform an action?

See comment

Describe the behaviour you'd like

Current alternative proposals:

@gtsiolis's comment

To access large workspaces and pay-as-you-go, first cancel your existing plan.
Existing plans will keep working until the end of March, 2023.

@jldec's comment, RFC (internal)

Describe alternatives you've considered

Additional context