fix(aws): make reading/writing of aws manifest consistent with other packages

[sl0thentr0py]

see the corresponding implementation here for all other packages:

craft/src/utils/registry.ts

Lines 41 to 43 in f4949f4

	JSON.parse(
	await fsPromises.readFile(packageManifestPath, { encoding: 'utf-8' })
	) || {},

craft/src/utils/registry.ts

Line 62 in f4949f4

const manifestString = JSON.stringify(updatedManifest, undefined, 2) + '\n';

mainly the newline at the end was missing which was causing the aws endpoint failures I think.

[BYK]

This should probably be extracted out as a helper to help with consistency?

[sl0thentr0py]

the helpers already exist in utils as linked above.. I don't know why whoever wrote the aws stuff didn't use them.
Don't really have time for a refactor here right now, sorry!