Add typing to iAPI's getConfig()

[Aljullu]

What?

Initially discussed in woocommerce/woocommerce@3b133f2#r165804930.

This PR types the Interactivity API's getConfig() function, similar to how it's done for getContext().

Why?

This allows consumers to consume it like this:

const config = getConfig< ConfigType >();

instead of missing the types or having to add a type assertion as

const config = getConfig() as ConfigType;

Testing Instructions

1. Add this code somewhere in the codebase:

type ConfigType = {
	prop: string;
};

const config = getConfig< ConfigType >();

2. Verify you don't get a TS error mentioning Expected 0 type arguments, but got 1..

[github-actions]

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[github-actions]

Flaky tests detected in 072e843.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/17763767596
📝 Reported issues:

• [Flaky Test] should refresh the page when stylesheet loading fails #71135 in /test/e2e/specs/interactivity/router-styles.spec.ts