saving tge current form before replacing it

[bamatic]

When performing upload-app-forms, and if the form to upload exists in the database

1. The current form is saved with it's attachments to a new doc of type="old-form" and doc_id="form:form_id"
2. All version of a given form can be obtained now getting all dos of type:"old-form" and doc_id="form:form_id"
3. attached xml files with the form definition are avaliable for each form version

This is related to #505

Is your feature request related to a problem? Please describe.
the cht-conf version 10 add the xml_version json key to the form doc when the action upload-app-forms is executed, but the new form of a given form._id replaces the old one and the old xml file is overwritten.
The cht add the form version of the form doc to its data_records.
If a data analyst found a trouble with a current form, he can always learn about collected data using the form, but if the problem is with historical old data, he knows fields sent into the data_record but he is not able to investigate data collection processus and for example, learn about how such a value is possible in a variable;

Describe the solution you'd like
We propose that upload-app-forms does not replace old version but :

before to the replacing, the old form is copied to a new doc but with type: "old-form" and the _id of replaced form is stored in the doc with type "old-form" using the key "doc-id";=:"form:formId", attachements, xml, form_html and model are saved to this type:"old-form" new doc
the form is replaced as now
Additional context
some endpoints could be added to the cht-core forms API to retrieve all versions of a given form:formID; and to get the xml file of a given form version something like GET api/v1/forms/{formid}.{format]/{sha1}