Add credit-bundle fleet size fields

[joshbwlng]

Change-type: minor

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WIP: Add credit bundle fleet size fields for credits runway calculator.

Checklist:

• [ ] Includes tests
• [x] Includes typings
• [ ] Includes updated documentation
• [ ] Includes updated build output

Depends on:

• https://github.com/balena-io/balena-api/pull/4248