[#774] feat: try to parse it as JSON

[chedieck]

Related to #774

Description

Allows the parsing of JSON strings.

Test plan

• If a paybutton is constructed with e.g. op-return='{"my": "customData"}"; we should be able to parse that into an object; that will later be broadcasted as

{
  my: 'customData'
}

... in a paybutton trigger.

• Also, I've added tests covering (what I thought to be) all the edge cases, if there is any weirdness missing from it please mention it.