🔨 Use ARM build of Postgis for development

Why:
- For a long time, Postgis has only offered official linux/amd64 Docker
  images, but now they're preparing to publish also linux/arm64 images.
    postgis/docker-postgis#216 (comment)
- On M3 Macbook, the ARM version is much faster than the x86 version:

"lein kaocha" test run before:

Total duration:  74,10113 seconds
207 tests, 1768 assertions, 0 failures.

Top 3 slowest kaocha.type/clojure.test (74,09882 seconds, 100,0% of total time)
  slow
    2,92415 seconds average (55,55887 seconds / 19 tests)
  e2e
    17,50770 seconds average (17,50770 seconds / 1 tests)
  fast
    0,02064 seconds average (1,03225 seconds / 50 tests)

...and after:

Total duration:  47,63434 seconds
207 tests, 1768 assertions, 0 failures.

Top 3 slowest kaocha.type/clojure.test (47,63207 seconds, 100,0% of total time)
  slow
    1,46157 seconds average (27,76986 seconds / 19 tests)
  e2e
    18,94063 seconds average (18,94063 seconds / 1 tests)
  fast
    0,01843 seconds average (0,92158 seconds / 50 tests)

docker-compose.yml

@@ -21,8 +21,13 @@ services:
       - "127.0.0.1:8080:8080"
       - "127.0.0.1:7000:7000"
 
+  # TODO: official arm64 build of postgis - currently using test builds
+  # https://github.com/postgis/docker-postgis/issues/216#issuecomment-2016916803
+  # https://github.com/postgis/docker-postgis/pull/356
+  # https://hub.docker.com/r/imresamu/postgis/tags
   db:
-    image: postgis/postgis:13-3.1
+    #image: postgis/postgis:13-3.1
+    image: imresamu/postgis:13-3.4
     environment:
       POSTGRES_USER: territorybro
       POSTGRES_PASSWORD: territorybro