LU-19007 doc: document client mount retry option

LU-19007 doc: document client mount retry option

Document the client mount retry option.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: Ib618a5e909b66136bb37ed82783af500cd6b40ee
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/59198
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Frederick Dilger <fdilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>