Re-allows ecco.cu-dbmi.dev to serve both the frontend and backend

[falquaddoomi]

When we transitioned from ecco.cu-dbmi.dev to coe-ecco.org, I made some changes that disabled the backend from being served from ecco.cu-dbmi.dev. This PR partially reverses those changes, so that coe-ecco.org served from Netlify can still access api.coe-ecco.org, and ecco.cu-dbmi.dev served from our ecco VM will now query ecco.cu-dbmi.dev/api.

In detail, this PR does the following:

• Instructs the frontend that's built on the ecco VM to consider itself served from ecco.cu-dbmi.dev and to query the API at ecco.cu-dbmi.dev/api
• Sets up nginx to allow backend access at /api/ again

I've tested that coe-ecco.org still works (it hits api.coe-ecco.org, which is still served from the ecco VM via its own server block, selected by hostname). I did a quick test on https://ecco.cu-dbmi.dev and verified that it also works: the frontend is querying ecco.cu-dbmi.dev/api, as it should, the backend is getting hit, and it's responding.

[netlify[bot]]

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