api: Updates to Makefile and configuration files.

- Re-organized and documented make targets.
- Parameterized the make targets to more cleanly support multiple
  development scenarios.
- Documented the different development scenarios in a README.
- Standardized the host port used when running locally.
- Updated DEV and PROD database config files to match current practice.
- Renamed `personal_measure_api.config.prod.json` to
  `personal_measure_api.config.docker.json` to more accurately reflect
  that this is the config used when building the docker image
  (regardless of which env it ends up in).

api/Dockerfile

@@ -16,7 +16,7 @@ RUN apk -v --update add --no-cache \
   postgresql-client
 
 COPY --from=build /pm-api/personal_measure_api /
-COPY personal_measure_api.config.prod.json /personal_measure_api.config.json
+COPY personal_measure_api.config.docker.json /personal_measure_api.config.json
 CMD ["/personal_measure_api", "serve"]
 
 # TODO: replace the above with something like: