form/fetch: href not updated when value is a method parameter

[kapouer]

When a page url is changed, candidate values in other blocks are found using "static" json schema.
However block types that have a field with $helper: 'service' (like fetch, api_form) have parameters fields that depend on which method is chosen.
The json schema to apply to these parameters is available in site.$services.

See

server/packages/api/services/page.js

Line 642 in 4b0c068

return Promise.all(Object.keys(hrefs).map(function(type) {