Add id to tilejson

[frodrigo]

Add the id field to tilejson output. So be able to retrieve the tilejson and rebuild the path to direct tilejson for further usage.

• On rendered it's on a add.
• On data it may override the id from the mbtiles.

[klokan]

Could you, please 🙏 , (ideally before making a pull request proposing a change in the software) make an issue explaining:

• what is the pain (=what is not possible to do right now with the software)
• why do you propose to do something (=reason, thoughts context)
• if you propose a solution (such as "Add id to tilejson") also what are all the advantages/benefits and perhaps disadvantages of your proposed change.

Then somebody can reasonably decide whether a pull request is meaningful and improves the software or not.

[frodrigo]

First I made code because I need it and plan to use it. Since I think it may benefit to other I share it as PR (and change is very small here). I personally think code is simpler to understand than long text explanation when diff is small.

So, actually /styles.json array share style id, but data and rendered (/index.json, /rendered.json; /data.json) are available as tilejson, without id.

I just need style, renderer and data id to store else where and to point later to unitary tilejson path. I need this in my UI. I also need it in my tile expirer to simply known the tile path and expire. To do it I get the id I added to the tilejson arrays.