fix(gatsby): better heuristic for automatic cache purging

[vladar]

Description

A follow up for #27549. That PR didn't take into account that the .cache directory exists in develop by the moment we call initialize. In develop the .cache directory is actually created here:

gatsby/packages/gatsby/src/commands/develop.ts

Lines 99 to 102 in ed31b35

	const tmpFileName = tmp.tmpNameSync({
	tmpdir: path.join(process.cwd(), `.cache`),
	})
	fs.outputFileSync(tmpFileName, this.script)

This PR uses a different heuristic to check for cache presence by just checking for .cache/json folder. We ensure this dir exists in the same initialize method, so it seems an appropriate target for this check:

gatsby/packages/gatsby/src/services/initialize.ts

Line 315 in ed31b35

await fs.ensureDirSync(`${cacheDirectory}/json`)

Related Issues

Fixes #27641