view-user: add --list-banks option

Problem: There is no concise way to view the banks that a user belongs
to.

Add a --list-banks optional argument to view-user, which will just print
the banks that a user belongs to in the flux-accounting database.

src/bindings/python/fluxacct/accounting/formatter.py

@@ -306,3 +306,21 @@ def __init__(self, cursor, username):
         super().__init__(
             cursor, error_msg=f"user {self.username} not found in association_table"
         )
+
+    def list_banks(self):
+        """
+        Return all of the banks that the user belongs to with each bank
+        on its own line.
+
+        Args:
+            username: the name of the user.
+        """
+        self.cursor.execute(
+            "SELECT bank FROM association_table WHERE username=?", (self.username,)
+        )
+        result = self.cursor.fetchall()
+        banks = ""
+        for bank in result:
+            banks += f"{str(bank[0])}\n"
+
+        return banks

src/bindings/python/fluxacct/accounting/user_subcommands.py

@@ -233,7 +233,7 @@ def clear_projects(conn, username, bank=None):
 #                   Subcommand Functions                      #
 #                                                             #
 ###############################################################
-def view_user(conn, user, parsable=False, cols=None):
+def view_user(conn, user, parsable=False, cols=None, list_banks=False):
     # use all column names if none are passed in
     cols = cols or fluxacct.accounting.ASSOCIATION_TABLE
 
@@ -250,6 +250,8 @@ def view_user(conn, user, parsable=False, cols=None):
         # initialize AssociationFormatter object
         formatter = fmt.AssociationFormatter(cur, user)
 
+        if list_banks:
+            return formatter.list_banks()
         if parsable:
             return formatter.as_table()
         return formatter.as_json()

src/cmd/flux-account-service.py

@@ -150,6 +150,7 @@ def view_user(self, handle, watcher, msg, arg):
                 msg.payload["username"],
                 msg.payload["parsable"],
                 msg.payload["fields"].split(",") if msg.payload.get("fields") else None,
+                msg.payload["list_banks"],
             )
 
             payload = {"view_user": val}

src/cmd/flux-account.py

@@ -57,6 +57,13 @@ def add_view_user_arg(subparsers):
             "MAX_CORES,QUEUES,PROJECTS,DEFAULT_PROJECT"
         ),
     )
+    subparser_view_user.add_argument(
+        "--list-banks",
+        action="store_const",
+        const=True,
+        help="list all of the banks a user belongs to",
+        metavar="LIST_BANKS",
+    )
 
 
 def add_add_user_arg(subparsers):