* feat: add pool_maxsize parameter to connection managers
Introduces the `pool_maxsize` parameter to `KeycloakOpenID` and `KeycloakAdmin` classes, allowing control over the underlying connection pool size in the `ConnectionManager`.
Adds corresponding tests to verify the parameter is correctly passed and stored for both synchronous and asynchronous clients.
* feat: apply pool maxsize for async as well
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Co-authored-by: Richard Nemeth <ryshoooo@gmail.com>