Add background-hash-mark addition for region routing

Per https://buymeacoffee.com/ripplebiz/region-filtering:

> After some discussions, and that there is some confusion
around #channels and #regions, it's been decided to drop
the requirement to have the '#' prefix. So, region names
will just be plain alphanumeric (and '-'), with no # prefix.

> For backwards compatibility, the names will internally have
a '#' prepended, but for all client GUI's and command lines,
you generally won't see mention of '#' prefixes. The next
firmware release (v1.12.0) and subsequent Ripple firmware
and Liam's app will have modified UI to remove the '#' requirement.

So, silently add, but don't duplicate, for users who have already
added hashmarks.

tests/test_send_messages.py

@@ -279,8 +279,8 @@ class TestOutgoingChannelBroadcast:
         mc = _make_mc(name="MyNode")
         chan_key = "de" * 16
         await ChannelRepository.upsert(key=chan_key, name="#flightless")
-        await ChannelRepository.update_flood_scope_override(chan_key, "#Esperance")
-        await AppSettingsRepository.update(flood_scope="#Baseline")
+        await ChannelRepository.update_flood_scope_override(chan_key, "Esperance")
+        await AppSettingsRepository.update(flood_scope="Baseline")
 
         with (
             patch("app.routers.messages.require_connected", return_value=mc),
@@ -303,8 +303,8 @@ class TestOutgoingChannelBroadcast:
         mc = _make_mc(name="MyNode")
         chan_key = "df" * 16
         await ChannelRepository.upsert(key=chan_key, name="#matching")
-        await ChannelRepository.update_flood_scope_override(chan_key, "#Esperance")
-        await AppSettingsRepository.update(flood_scope="#Esperance")
+        await ChannelRepository.update_flood_scope_override(chan_key, "Esperance")
+        await AppSettingsRepository.update(flood_scope="Esperance")
 
         with (
             patch("app.routers.messages.require_connected", return_value=mc),