Mint short links on piha.lc / beta.piha.li (#12)

## Summary
- Point `SHORTENER_BASE_URL` at `https://piha.lc` (prod) and `https://beta.piha.li` (beta).
- Stop documenting `shortener.aimloperations.com` as the mint host.

Closes #11.

Depends on url_shortening_service serving `/api/` on the short host.

## Test plan
- [ ] Set `SHORTENER_BASE_URL=https://beta.piha.li` and matching token in beta env
- [ ] Compose a campaign SMS and confirm mint hits beta.piha.li (not shortener-beta)
- [ ] Body contains `https://beta.piha.li/<code>`

Reviewed-on: #12

site/messaging/tests.py

@@ -1598,7 +1598,7 @@ class CampaignUtmLinkTests(TestCase):
         }
         with self.settings(
             PUBLIC_SITE_URL="https://mkdrealtor.com",
-            SHORTENER_BASE_URL="https://shortener.aimloperations.com",
+            SHORTENER_BASE_URL="https://piha.lc",
             SHORTENER_API_TOKEN="monica:test-token",
         ):
             with patch(
@@ -1630,7 +1630,7 @@ class CampaignUtmLinkTests(TestCase):
         mock.text = '{"detail":"Unauthorized"}'
         with self.settings(
             PUBLIC_SITE_URL="https://mkdrealtor.com",
-            SHORTENER_BASE_URL="https://shortener.aimloperations.com",
+            SHORTENER_BASE_URL="https://piha.lc",
             SHORTENER_API_TOKEN="monica:bad",
         ):
             with patch("messaging.shortener.requests.post", return_value=mock):
@@ -1687,7 +1687,7 @@ class CampaignUtmLinkTests(TestCase):
         url = reverse("messaging:campaign_short_link")
         with self.settings(
             PUBLIC_SITE_URL="https://mkdrealtor.com",
-            SHORTENER_BASE_URL="https://shortener.aimloperations.com",
+            SHORTENER_BASE_URL="https://piha.lc",
             SHORTENER_API_TOKEN="monica:test-token",
         ):
             with patch("messaging.shortener.requests.post", return_value=mock):