storage-users: Add config option for graceful shutdown timeout

[rhafer]

Add STORAGE_USERS_GRACEFUL_SHUTDOWN_TIMEOUT setting to allow an graceful shutdown of the storage-users service. This currently only applicable when running storage-user as a sepearate service.

Setting STORAGE_USERS_GRACEFUL_SHUTDOWN_TIMEOUT to a non-zero value gives the storage-users service a chance to cleanly shutdown and finish any in progess tasks (e.g. metadata propagation) before exiting.

Partial-Fix: #6602

Keeping this in draft for now, until the relate reva part is merged (cs3org/reva#4072)

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[mmattel]

As just discussed with @rhafer, I am working on a commit to update the envvar text and a readme addon with an explanation. commit will come latest tomorrow morning.

[mmattel]

@saw-jan did some tests to proof my writing:

This is how I run:
start default services expect storage-users
OCIS_EXCLUDE_RUN_SERVICES=storage-users \  
./bin/ocis server

start storage-users in another terminal
STORAGE_USERS_GRACEFUL_SHUTDOWN_TIMEOUT=5 \
STORAGE_USERS_LOG_LEVEL=debug \
./bin/ocis storage-users server

I just hit ctrl+c

...preparing for a graceful shutdown with deadline
...gracefully closed
...shutting down in 4 seconds

[saw-jan]

@saw-jan did some tests to proof my writing:

This is how I run:
start default services expect storage-users
OCIS_EXCLUDE_RUN_SERVICES=storage-users \  
./bin/ocis server

start storage-users in another terminal
STORAGE_USERS_GRACEFUL_SHUTDOWN_TIMEOUT=5 \
STORAGE_USERS_LOG_LEVEL=debug \
./bin/ocis storage-users server

I just hit ctrl+c

...preparing for a graceful shutdown with deadline
...gracefully closed
...shutting down in 4 seconds

Command kill <pid> will terminated the service immediately

[1]    174239 terminated  STORAGE_USERS_GRACEFUL_SHUTDOWN_TIMEOUT=5 STORAGE_USERS_LOG_LEVEL=debug

[mmattel]

Command kill will terminated the service immediately

good point, will add that.

[sonarcloud]

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[mmattel]

LGTM from a docs pov 👍