Allow option to read from stdin as opposed required a file

[ghostsquad]

Enhancement

This is proposed enhancement is to allow KCL to read from stdin as opposed to requiring a file. Here are some possible implementations:

kcl run - << EOF
{
  foo: "bar"
}
EOF

Allow stdin as well as other files

kcl run - foo.k << EOF
{
  foo: "bar"
}
EOF