Adding new feature to track user all processes on memleak

Current memleak need to specify the user process pid or command to track all user processes.
Which means, it could track only one user process at a time.
How about add `-u` option for memleak to track every user process memory allocation?
Or make new tool name `allocsnoop`?

It seems pretty hard to add `-u` option on memleak,
since memleak uses `address` as a key of `allocs` `BPF_HASH` but address could conflict between user processes.
It could be possible to implement `-u` option easily, if the key of `combined_allocs` `BPF_HASH`(=`stack_id`) doesn't conflict between user processes.

Start by reading the memleak implementation and the allocs and combined_allocs BPF_HASH definitions mentioned in the issue. Compare the proposed -u option with the alternative allocsnoop tool, then establish a decided design for tracking every process owned by a user without key collisions. Done should include an agreed implementation scope and validation for multi-process tracking.

Written by the indexing model from the issue text.