Define prop naming conventions

## What
We should have a common way of translating base/modifier classes that exist in vanilla to props in `react-components`.

For example, the `help` prop in `Input` could be named `formHelpText` instead to match `p-form-help-text` from Vanilla.
There are many examples for inconsistencies like that.

## Why
This would make working with react-components more intuitive for people who are already familiar with the vanilla framework (and vice-versa).

## Other considerations
If we agree on a naming convention it might be worth updating all components props at some point even though there will be breaking changes.

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Originally raised by @bartaz https://github.com/canonical-web-and-design/react-components/pull/761#discussion_r850305544