Enable pronoun substitution in get_bz_params() for efficient filtering

[benjaminmah]

BMO supports pronoun substitution (e.g. %assignee% for the bug assignee as per BMO documentation), which can improve rule efficiency.

Currently, in scripts like uplift_beta.py, a separate filter is applied after retrieving bugs. By using pronoun substitution, we could directly filter for bugs with a needinfo requestee matching the assignee, potentially streamlining the process.

This approach requires investigation to confirm functionality, however.