Fix alignment in charts endpoint

[thiagoftsm]

Summary

Our current json output for chart labels is not aligned, because we are missing a tab:

                        "green": null,
			"red": null,
			"alarms": {

			},
			"chart_labels": {
		"123caniuse":"testing",
		"myconstant":"never_change",
		"ourconstant":"we talk about",
		"yourconstant":"you define"
			}

This PR is fixing this issue aligning the JSON:

                        "green": null,
			"red": null,
			"alarms": {

			},
			"chart_labels": {
				"123caniuse":"testing",
				"myconstant":"never_change",
				"ourconstant":"we talk about",
				"yourconstant":"you define"
			}

Test Plan

1. Before to compile this branch, start your netdata and access http://localhost:19999/api/v1/charts?all, you will have chart labels not aligned.
2. Compile this branch
3. Access the link again https://localhost:19999/api/v1/charts?all (press Ctrl+R) and you will see that chart labels are now aligned.

Additional Information

For users: How does this change affect me?

Describe the PR affects users: - Which area of Netdata is affected by the change? API - Can they see the change or is it an under the hood? If they can see it, where? It is not visible for uses - How is the user impacted by the change? When users work directly with API, they will have data better organized. - What are there any benefits of the change? It keeps the JSON cleaner.