Prevent sqlalchemy's lack of url encoding from leaking passwords

Switches away from using `str(engine_instance.engine)` for rendering
connection strings, in order to prevent passwords containing
characters such as `#` from leaking. The name of the segment will
contain the password if this character is used, likely others as well.

See: https://bugs.python.org/issue18140 and encode/database#145

The code in question is here:

sqlalchemy/sqlalchemy/blob/aea28a9/lib/sqlalchemy/engine/url.py#L597-L630

aws_xray_sdk/ext/sqlalchemy_core/patch.py

@@ -14,7 +14,7 @@
 def _sql_meta(engine_instance, args):
     try:
         metadata = {}
-        url = urlparse(str(engine_instance.engine.url))
+        url = urlparse(engine_instance.engine.render_as_string())
         # Add Scheme to uses_netloc or // will be missing from url.
         uses_netloc.append(url.scheme)
         if url.password is None: