Let people name accounts and use the names to tell accounts apart

Connections get an account_name (migration 0039) that the owner sets with
PATCH /api/connections/<id>; the account label stays the account's
identity, so signing in again still finds it. When someone has more than
one account of a service, its tools are listed as "Telegram · <account>"
and the model sees each account's actions under the account's name
(telegram_send_message_alerts_bot) with the account in the description,
instead of _1 and _2. Actions shared by different services are named
after the service. Tools a user renamed keep their name.

docsgpt/storage/db/models.py

@@ -608,6 +608,9 @@ connector_sessions_table = Table(
     Column("scopes", JSONB, nullable=False, server_default="[]"),
     Column("last_error", Text),
     Column("last_used_at", DateTime(timezone=True)),
+    # Added in ``0039_connection_account_name``: what the user calls the
+    # account; ``account_label`` stays its identity.
+    Column("account_name", Text),
 )