Add proposed release managers for 9.4 and 9.5

Here is a proposed plan for 9.4 and 9.5. Let me know if you have any conflicts/issues/etc.:

/cc: @annabeldunstone, @psimyn, @mikegreiling, @jamedjo, @jneen, @jarka, @smcgivern, @DouweM, @jschatz1, @timzallmann