Fix Observations Layer tab data loading

[rajadain]

Overview

This bug was introduced in 02b5a7f. Allows the Observations Layer tab to load historical data again.

Connects #2761

Notes

The historical data loading still often fails because of server issues.

Testing Instructions

• Check out this branch and bundle
• Open the app and the javascript console
• Go to the observations tab in the layer picker and enable a layer
• Click an observation point and click through to Historical Data
• Ensure there are no javascript errors in the console (disregard any server side errors)

[kellyi]

Setting this up!

[kellyi]

Was able to get River Gauge historical data to load:

The other observation layers seemed to send back 500 errors from the server -- not sure whether those originate from MMW or from the observations service?

[kellyi]

👍 from me. I assume we're not dealing with the server side errors here, but if we have some control over those we should consider making a card to fix them.

[rajadain]

Correct: we are not touching the server side at all here, just the client side. We may move away from the backend service used for this in the future, so I'm not going to make a card for the intermittent failures right now. It is a known issue.

Thanks for taking a look!