[PROPOSAL] Mask http

# New mask HTTP

```yaml
- selector:
# the . (dot) selector should select the whole dictionary, so the http response will replace the input
jsonpath: "."
mask:
http:
method: get
url: https://www.data.gouv.fr/api/1/users/{{.userid}}/
# auth:
# headers:
- selector:
jsonpath: "first_name"
mask:
randomChoiceInUri: pimo://nameFR
```

No source file or test is named. Start by tracing how YAML selector entries and existing mask types are parsed, then compare the proposed `http` configuration with the `randomChoiceInUri` example. Done should match the shown behavior: the `.` selector uses the HTTP response as input, with the URL's `{{.userid}}` value resolved.

Written by the indexing model from the issue text.