Currently, if we run `param set guestbook-ui foo-bar x`,

The jsonnet snippet will write: `foo-bar: "x"`.

However, this is incorrect jsonnet syntax. This commit will fix this
issue, to instead write `"foo-bar": "x"`.

Also updates the `Get...` Param functions to return non-quoted
identifiers for prettier display.

Signed-off-by: Jessica Yuen <im.jessicayuen@gmail.com>