fix(telemetry): fix isTrackingEnabled always truthy

[AhsanAyaz]

Fixed the isTrackingEnabled being exported as a function returning a function instead of a function returning a value

Description

As #22531 mentions, the telemetry module is exporting a function that returns a function instead of a function that returns a boolean value.
I've gone through the entire codebase, we don't use it as a returning function anywhere.

Also, added a minor test for telemetry.js

Documentation

Related Issues

Fixes #22531

[AhsanAyaz]

@LekoArts can you review if everything looks fine with this one?

[pieh]

Yup, thanks for catching it!

TBF, we still didn't emit any data (we just unnecessarily processed aggregated stats for file sizes in

gatsby/packages/gatsby/src/commands/build.js

Lines 142 to 155 in 2cefdcb

	if (telemetry.isTrackingEnabled()) {
	// transform asset size to kB (from bytes) to fit 64 bit to numbers
	const bundleSizes = stats
	.toJson({ assets: true })
	.assets.filter(asset => asset.name.endsWith(`.js`))
	.map(asset => asset.size / 1000)
	const pageDataSizes = [...store.getState().pageDataStats.values()]
	telemetry.addSiteMeasurement(`BUILD_END`, {
	bundleStats: telemetry.aggregateStats(bundleSizes),
	pageDataStats: telemetry.aggregateStats(pageDataSizes),
	queryStats: graphqlRunner.getStats(),
	})
	}

)

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