postfix: allow qmgr to delete mails in bounce/ directory

[rmetrich]

See RHEL-30271 - postfix qmgr cannot delete mails in bounce/ directory.

AVC:

... type=PROCTITLE msg=...: proctitle=qmgr-l-tunix-u
... type=PATH msg=...: item=1 name=bounce/E40A741281B ... obj=system_u:object_r:postfix_spool_bounce_t:s0 nametype=DELETE cap_fp=0 cap_fi=0 cap_fe=0 cap_fver=0 cap_frootid=0
... type=PATH msg=...: item=0 name=bounce/ ... obj=system_u:object_r:postfix_spool_bounce_t:s0 nametype=PARENT cap_fp=0 cap_fi=0 cap_fe=0 cap_fver=0 cap_frootid=0
... type=CWD msg=...: cwd=/var/spool/postfix
... type=SYSCALL msg=...: arch=c000003e syscall=87 success=no exit=-13 ... comm=qmgr exe=/usr/libexec/postfix/qmgr subj=system_u:system_r:postfix_qmgr_t:s0 key=(null)
... type=AVC msg=...: avc:  denied  { write } for  pid=2012444 comm=qmgr name=bounce ... scontext=system_u:system_r:postfix_qmgr_t:s0 tcontext=system_u:object_r:postfix_spool_bounce_t:s0 tclass=dir permissive=0

[zpytela]

Merging, thank you.