fix(outputTemplate): unescape string output

[reubenmiller]

When using an output template which references a body which has non-json text, the output does not print out newline literals (due to a double json encoding problem).

For example the following command builds custom output from an event's binary file.

c8y events downloadBinary --id 93268 --outputTemplate "response.body"

Before

[[files]]\npath = \"/etc/tedge/tedge.toml\"\ntype = \"tedge.toml\"\n\n[[files]]\npath = \"/etc/tedge/mosquitto-conf/tedge-mosquitto.conf\"\ntype = \"tedge-mosquitto.conf\"\n\n[[files]]\npath = \"/etc/tedge/plugins/tedge-log-plugin.toml\"\ntype = \"tedge-log-plugin\"\nuser = \"tedge\"\ngroup = \"tedge\"\nmode = 0o0644\n

After

[[files]]
path = "/etc/tedge/tedge.toml"
type = "tedge.toml"

[[files]]
path = "/etc/tedge/mosquitto-conf/tedge-mosquitto.conf"
type = "tedge-mosquitto.conf"

[[files]]
path = "/etc/tedge/plugins/tedge-log-plugin.toml"
type = "tedge-log-plugin"
user = "tedge"
group = "tedge"
mode = 0o0644