openmaptiles-tools: consider MIN_ZOOM/MAX_ZOOM env (#992)

Allow MIN_ZOOM, and MAX_ZOOM to be overwritten from shell for `quickstart.sh`, `make generate-dc-config`, and other `docker-compose openmaptiles-tools` uses.

For example,
```
export MAX_ZOOM=14; ./quickstart.sh monaco
```
ignores the `MAX_ZOOM=14` environment variable and uses the `MAX_ZOOM=7` value from `.env` file

This PR will also make this code unecessary
5c640daf4f/.github/workflows/tests.yml (L26-L28)

docker-compose.yml

@@ -34,8 +34,10 @@ services:
       # Must match the version of this file (first line)
       # download-osm will use it when generating a composer file
       MAKE_DC_VERSION: "2.3"
-      # Allow DIFF_MODE to be overwritten from shell
+      # Allow DIFF_MODE, MIN_ZOOM, and MAX_ZOOM to be overwritten from shell
       DIFF_MODE: ${DIFF_MODE}
+      MIN_ZOOM: ${MIN_ZOOM}
+      MAX_ZOOM: ${MAX_ZOOM}
       # Imposm configuration file describes how to load updates when enabled
       IMPOSM_CONFIG_FILE: ${IMPOSM_CONFIG_FILE}
       # Which files to use during import-borders processing