Use `SetEscapeHTML` when marshalling JSON everywhere

[mihaitodor]

Following up on #1244, as discussed on Discord, we want to set SetEscapeHTML when marshalling JSON to avoid certain characters, namely &, < and >, being escaped to \u0026, \u003c and \u003e.

For now, this impacts the following, but I could be missing others:

• string() - Leverages Gabs here
• format_json() - Uses the Go json lib directly, but doesn't set this flag
• this.bytes() triggers it too, but need to dig into it to see why

Workarounds:

• this.string().replace_all_many(["\\u0026", "&", "\\u003c", "<", "\\u003e", ">"])
• A new escape_html flag (default true) was added to format_json() in Add escape_html parameter to the format_json bloblang method benthos#39