docs: release 1.2.0 and unpin downstream from the 1.1 series

Issue #10 Task 6. The install pin moves from ==1.1.* to >=1.2,<2 - left
alone, everyone following the README would have stayed silently on
1.1.2 without this fix and without a warning. Telemetry field count
re-measured via inspect.signature: still 22.

src/polygateway/__init__.py

@@ -32,7 +32,7 @@ from polygateway.types import (
     SourceConfig,
 )
 
-__version__ = "1.1.2"
+__version__ = "1.2.0"
 
 __all__ = [
     "DEFAULT_PROFILES",