docs: fix RGW AWS credential export commands
docs: fix RGW AWS credential export commands

Fix ceph rgw export commands to access values in object yaml definitions through jsonpath instead of grep. This solves issues that arise, should there be more than one lines with the grep value in the yaml file which would concatenate arbitrary values.

Closes: https://github.com/rook/rook/issues/6087
Signed-off-by: Daniel Schneider <9b563c3bb5824a8fe2525739ff1921860c7a4354@eramux.com>

rook/rook,rook/rook,rook/rook,rook/rook,rook/nfs,rook/nfs,rook/rook,rook/nfs