add yaml file with nshms to use

nshms.yml

+####
+# NSHMs to use for unit tests and for deployments.
+####
+nshms:
+  # Alaska 2023 NSHM
+  -
+    repo: nshm-alaska
+    tag: 3.a.0
+    year: 2023
+    deployments:
+      - development
+      - staging
+      # TODO: Add to production when model is stable
+      # - production
+
+  # CONUS 2018 NSHM
+  -
+    repo: nshm-conus
+    tag: 5.2.0
+    year: 2018
+    deployments:
+      - development
+      - staging
+      - production
+
+  # CONUS 2023 NSHM
+  -
+    repo: nshm-conus
+    tag: 6.a.3
+    year: 2023
+    deployments:
+      - development
+      - staging
+      # TODO: Add to production when model is stable
+      # - production
+
+  # Hawaii 2021 NSHM
+  -
+    repo: nshm-hawaii
+    tag: 2.0.2
+    year: 2021
+    deployments:
+      - development
+      - staging
+      - production