Add a task showing usage of if with nontrivial schema

[erosb]

Suggested by Sandrina Pereira on Slack:

Still about Conditionals, at Remote most engineers struggle to understand what's possible in if schemas. They think it's just const, but it's basically anything really. minimum, contains, pattern, not, etc. So an extra example showing it would be useful.

[LasneF]

even more the sample provided looks wrong ! it misses that required : ["isFullTime"]

that is not obvious at all as we could think that the properties make it mandatory (by magic :) )

{
  "type": "object",
  "properties": {...},
  "if": {"properties": {"isFullTime": {"const": true}}},
  "then": {"required": ["salary"]},
}