rgw: add CORTX Motr SAL implementation

rgw: add CORTX Motr SAL implementation

To build with Motr backend, use -DWITH_RADOSGW_MOTR=YES cmake
option. cortx-motr-devel rpm should be installed beforehand.

To connect to Motr cluster, add the following configuration
parameters to ceph.conf:

    [client]
            ...
            rgw backend store = motr
            motr profile fid  = 0x7000000000000001:0x4f
            motr ha endpoint  = inet:tcp:10.0.0.1@2001
    ...
    [client.rgw.8000]
            ...
            motr my endpoint  = inet:tcp:10.0.0.1@5001
            motr my fid       = 0x7200000000000001:0x29

The correct values for the Motr connection parameters can be
taken from `hctl status` cmd output after Motr cluster is
bootstrapped. In the example above, the values were taken from
the following output:

    Profile:
        0x7000000000000001:0x4f
    Services:
        centos8n1
        [started] hax       0x7200000000000001:0x6  inet:tcp:10.0.0.1@5001
        ...
        [unknown] m0_client 0x7200000000000001:0x29 inet:tcp:10.0.0.1@5001

Motr pkgs for the build/run can be taken from
https://github.com/Seagate/cortx-motr/releases/tag/2.0.0-rgw.

Co-authored-by: Sining Wu <sining.wu@seagate.com>
Signed-off-by: Andriy Tkachuk <andriy.tkachuk@seagate.com>