Improve typing and docs recommendation

[mkszepp]

During some tests inside my app, i think its better to hold the app.ts file cleaner and moving setups to an extra file like we did before.

In additional we need to allow passing IconDefinition as @icon to component.
We have already a use case for that inside test-app and maybe peoples were already using it.
Passing IconDefinition is very interesting, when consumer apps are using template-tag (strict mode) in ember (which is part of polaris edition and can be used already), because this make at the end the font-awesome.ts nearly unnecessary (just the setup for faConfig.autoAddCss = false; is needed.
Its more a choise for consumer apps, if they want register icons and consume with string or importing icon directly at each point.

Changes in this PR:

• Improve typing inside icon component
• allow passing IconDefinition
• Update docs setup and apply changes to test-app
• Add note for passing IconDefinition

[mkszepp]

@robmadole these are the final changes. Once this is merged, we’ll be ready for release.

Before merging, I’ll update the release date in the changelog.

Let me know if you’d like to add or change anything before we proceed with the release.

[mkszepp]

Added installation for using inside .gjs/.gts and marked as recommended installation way, as there was someone asking how it works with v2 #246