Add manager graceful shutdown, timeout, and wait

As per the part1 of the graceful shutdown timeouts[1], this commit
add/modifies the below timeout/wait needed for graceful shutdown:

- Override the default of the graceful_shutdown_timeout to 180.
- Add a new config option for manager shutdown timeout.

It also adds a graceful_shutdown() method on the manager side, which
will be called by the nova/service.py->stop() method before it stops
the 2nd RPC server. In part1, this will wait for the configurable wait
time, but part2 will implement a better solution to track the
in-progress tasks. The idea is to have this single interface from the
service manager (graceful_shutdown()) that will be called during
graceful shutdown and is responsible for finishing the required tasks
and cleanup.

Partial implement blueprint nova-services-graceful-shutdown-part1

[1] https://specs.openstack.org/openstack/nova-specs/specs/2026.1/approved/nova-services-graceful-shutdown-part1.html#graceful-shutdown-timeouts

Change-Id: I7c1934d3ec7854feac3fc8432627c25eba963ddf
Signed-off-by: Ghanshyam Maan <gmaan.os14@gmail.com>

requirements.txt

@@ -43,7 +43,7 @@ oslo.messaging>=14.1.0 # Apache-2.0
 oslo.policy>=4.5.0 # Apache-2.0
 oslo.privsep>=2.6.2 # Apache-2.0
 oslo.i18n>=5.1.0 # Apache-2.0
-oslo.service[threading]>=4.4.1 # Apache-2.0
+oslo.service[threading]>=4.5.0 # Apache-2.0
 rfc3986>=1.2.0 # Apache-2.0
 oslo.middleware>=3.31.0 # Apache-2.0
 psutil>=3.2.2 # BSD