Keep existing snowflake user power levels around on Matrix

Keep existing snowflake user power levels around on Matrix

We have some snowflake Matrix room permissions setup for some particular communities to be able to self-manage and moderate. Avoid regressing them back to defaults.

Follow-up to !2303 (merged)

Dev notes

Windows:

// --keep-existing-user-power-levels=1 (defaults to 1/true)
set matrix__bridge__applicationServicePort=9001&&node ./scripts/utils/ensure-existing-bridged-matrix-room-up-to-date.js --uri MadLittleMods/hhstrhtrdehhrtdhtrh

// --keep-existing-user-power-levels=0
set matrix__bridge__applicationServicePort=9001&&node .\scripts\utils\ensure-existing-bridged-matrix-room-up-to-date.js --uri MadLittleMods/hhstrhtrdehhrtdhtrh --keep-existing-user-power-levels=false