run: Add -o argument to list realms with stored zuliprc.

Tests updated.

tests/cli/test_run.py

@@ -133,6 +133,7 @@ def test_main_help(capsys: CaptureFixture[str], options: str) -> None:
         "--theme THEME, -t THEME",
         "-h, --help",
         "-d, --debug",
+        "-o, --list-organizations",
         "--list-themes",
         "--profile",
         "--config-file CONFIG_FILE, -c CONFIG_FILE",

zulipterminal/cli/run.py

@@ -150,6 +150,12 @@ def parse_args(argv: List[str]) -> argparse.Namespace:
         help="config file downloaded from your zulip "
         "organization (default: ~/zuliprc)",
     )
+    parser.add_argument(
+        "-o",
+        "--list-organizations",
+        action="store_true",
+        help="list all the organizations that you have configurations for, and exit",
+    )
     parser.add_argument(
         "--theme",
         "-t",
@@ -455,6 +461,16 @@ def list_themes() -> str:
     )
 
 
+def list_realms() -> str:
+    valid_orgs = [
+        file.parent.name for file in Path(ZULIP_CONFIG_PATH).glob("*/zuliprc")
+    ]
+    if len(valid_orgs) == 0:
+        exit_with_error("No organizations found in zuliprc config folder.")
+    text = "The following organizations are available:\n  "
+    return text + "\n  ".join(valid_orgs)
+
+
 def path_to_realm_zuliprc(realm_name_prefix: str) -> str:
     if len(realm_name_prefix) < 3:
         exit_with_error("Organization name prefix must be at least 3 characters long")
@@ -513,6 +529,10 @@ def main(options: Optional[List[str]] = None) -> None:
         print(f"Zulip Terminal {ZT_VERSION}")
         sys.exit(0)
 
+    if args.list_organizations:
+        print(list_realms())
+        sys.exit(0)
+
     if args.list_themes:
         print(list_themes())
         sys.exit(0)