docs: Document ability to configure lease time
docs: Document ability to configure lease time

In v6.3.0-rc1~64 we've introduced ability to configure lease
time, but forgot to document the feature. Let's fix that.

Fixes: 97a0aa246799c97d0a9ca9ecd6b4fd932ae4756c
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1908631
Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Daniel P. Berrangé <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

zippy2/libvirt,nertpinx/libvirt,olafhering/libvirt,nertpinx/libvirt,jfehlig/libvirt,nertpinx/libvirt,olafhering/libvirt,jfehlig/libvirt,crobinso/libvirt,libvirt/libvirt,crobinso/libvirt,libvirt/libvirt,jfehlig/libvirt,jfehlig/libvirt,crobinso/libvirt,libvirt/libvirt,olafhering/libvirt,nertpinx/libvirt,zippy2/libvirt,zippy2/libvirt,zippy2/libvirt,libvirt/libvirt,nertpinx/libvirt,crobinso/libvirt,olafhering/libvirt