Get "secrets" from something other than the `operations` repo

We'd like to make this repo self-contained and remove operations repo dependence. Some annoyances with the operations repo dependence:

• dependency updates are harder (see for example, the need to do simultaneous PRs in both repos cmu-delphi/operations#70 and #935, in order to update dependencies)
• setup changes are harder (see for example, the work here that needs to change the setup.sh script in operations)

Merging Dockerfiles:

• #1000 made the db Docker image self-contained in this repo
• #1043 made the delphi_wb Docker image self-contained in this repo

What other work is there that needs doing?

Other repos using operations repo Dockerfiles (this is an organization-wide codebase search query):

• delphi-epidata-private
• www-epicast
• flu-contest