Environment variables documentation (#1089)

* Created environment variables documentation

* Removed table + Listed variable names under respective sections

* Removed individually listed environment variables

If included, then it won't be up-to-date if we update / remove variables and will need to update this everytime.
Hence removing the specific names of environment variables.

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Co-authored-by: Mahadik, Mukul Chandrakant <MukulChandrakant.Mahadik@nrel.gov>

docs/dev/back/config_environment_variables.md

@@ -0,0 +1,15 @@
+# Configuring Environment Variables
+
+The search results below identify some environment variables that need to be manually configured.
+
+#### DB, Webserver, Push Config
+- Use this [search](https://github.com/search?q=repo%3Ae-mission%2Fe-mission-server+%2Fconfig.get%5C%28%5C%22%5BA-Z%5D%2F&type=code) to obtain usage of `DB, WEBSERVER, PUSH` environment variables in the [e-mission-server](https://github.com/e-mission/e-mission-server) repository.
+
+#### AWS Cognito Credentials
+
+- Use this [search](https://github.com/search?q=repo%3Ae-mission%2Fop-admin-dashboard+%2F.getenv%5C%28%5C%22%5BA-Z%5D%2F&type=code) to obtain usage of `COGNITO` variables in the [admin-dashboard](https://github.com/e-mission/op-admin-dashboard) repository.
+
+#### Overpass, Nominatim, Geofabrik
+
+- Use this [search](https://github.com/search?q=repo%3Ae-mission%2Fe-mission-server+%2F.environ.get%5C%28%5C%22%5BA-Z%5D%2F&type=code) to obtain usage of `Overpass, Nominatim, Geofabrik` environment variables in the [e-mission-server](https://github.com/e-mission/e-mission-server) repository.
+- Use this [search](https://github.com/search?q=repo%3Ae-mission%2Fe-mission-server+geofabrik&type=code) to view some variables that are set using GitHub secrets in the [e-mission-server](https://github.com/e-mission/e-mission-server) GitHub workflows.