Add support for a .local.envrc file

As this is useful when setting custom configuration.

.envrc

@@ -3,3 +3,7 @@ use guix -l guix-dev.scm --ad-hoc postgresql
 export GUILE_LOAD_COMPILED_PATH="$PWD:$GUILE_LOAD_COMPILED_PATH"
 export GUILE_LOAD_PATH="$PWD:$GUILE_LOAD_PATH"
 export PATH="$PWD/scripts:$PATH"
+
+if [ -f .local.envrc ]; then
+  source_env .local.envrc
+fi

.gitignore

@@ -21,3 +21,5 @@ scripts/guix-data-service-process-jobs
 scripts/guix-data-service-query-build-servers
 scripts/guix-data-service-process-branch-updated-email
 pre-inst-env
+
+.local.envrc