provide kdumpctl get-default-crashkernel for kdump_anaconda_addon and RPM scriptlet
    
    Resolves: bz1895258
    Upstream: Fedora
    Conflict: None
    
    commit 796d0f6fd2932fd7c009f4517133b1a9c39501e5
    Author: Coiby Xu <coxu@redhat.com>
    Date:   Tue Nov 16 12:23:02 2021 +0800
    
        provide kdumpctl get-default-crashkernel for kdump_anaconda_addon and RPM scriptlet
    
        Provide "kdumpctl get-default-crashkernel" for kdump_anaconda_addon
        so crashkernel.default isn't needed.
    
        When fadump is on, kdump_anaconda_addon would need to specify the dump
        mode, i.e. "kdumpctl get-default-crashkernel fadump".
    
        This interface would also be used by RPM scriptlet [1] to fetch default
        crashkernel value.
    
        [1] https://docs.fedoraproject.org/en-US/packaging-guidelines/Scriptlets/
    
        Reviewed-by: Pingfan Liu <piliu@redhat.com>
        Reviewed-by: Philipp Rudo <prudo@redhat.com>
        Signed-off-by: Coiby Xu <coxu@redhat.com>
    
    Signed-off-by: Coiby Xu <coxu@redhat.com>