Update ortho layers to include most recent

[hannahkates]

Necessary work:

• Backend work to include this layer in the layers API. Draft PR for that add 2018 aerials from DoITT labs-layers-api#175
• Frontend changes to consume the 2018 aerials layer and include it in the checklist

[allthesignals]

Looks like we just need to try out the PR: NYCPlanning/labs-layers-api#175

Nothing should need to happen in ZoLa to get it to appear — it just displays whatever's provided by the layers-api.

[mtreg]

Was looking for the more recent imagery in ZOLA - at least 2018, as it seems DoITT hasn't made the 2020 imagery available as a tile layer yet (last I had checked). I was going to submit an issue on this front but came across this one so adding a comment here - not sure how widely of interest this would be, but keeping ZOLA up to date in terms of the aerial imagery avaialble for viewing would definitely be helpful for some.

And for what its worth, the imagery is also available as WMS/WMTS layers from NYS - https://orthos.its.ny.gov/arcgis/rest/services/wms - the imagery is served out by year, for whatever areas of the state have had imagery collected, so for years like 2020, 2018, 2016, etc., I believe NYC imagery is included in it.

For example, I can load the color 2020 imagery into QGIS as a WMS/WMTS layer based on this URL https://orthos.its.ny.gov/arcgis/rest/services/wms/2020/MapServer/WMTS/1.0.0/WMTSCapabilities.xml
(the color infrared is available from https://orthos.its.ny.gov/arcgis/rest/services/wms/2020_cir/MapServer/WMTS/1.0.0/WMTSCapabilities.xml)