update kexec-kdump-howto
    
    Resolves: bz2059492
    Upstream: Fedora
    Conflict: None
    
    commit 1e7df3e1f355da4fe0eca6422479963f7e772bf8
    Author: Coiby Xu <coxu@redhat.com>
    Date:   Tue Mar 1 17:30:50 2022 +0800
    
        update kexec-kdump-howto
    
        1. yum is deprecated so use dnf instead
        2. use the "kdumpctl reset-crashkernel" API
        3. ask the users to refer to crashkernel-howto.txt for setting custom
           crashkernel value
        4. fix a typo
    
        Philipp Rudo <prudo@redhat.com>
    
        Signed-off-by: Coiby Xu <coxu@redhat.com>
    
    Signed-off-by: Coiby Xu <coxu@redhat.com>