new: support metadata kind email

[florianm]

This PR breaks the support of email out of #284.

• Close Support all metadata kinds: email, phoneNumber, audit, etc #209 (audit is not really a metadata kind as it behaves differently)
• Audit will be addressed in a separate PR as alternative to new: metadata kind email and new control for Audit #284
• Two small changes are added, one to add "email" as available metadata kind, the second to populate the binding.
• The changes are analogous to other metadata kinds, e.g. username.

A simple form with a metadata field "email" and a text field:

<h:html xmlns="http://www.w3.org/2002/xforms" xmlns:h="http://www.w3.org/1999/xhtml" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:jr="http://openrosa.org/javarosa" xmlns:ev="http://www.w3.org/2001/xml-events" xmlns:orx="http://openrosa.org/xforms" xmlns:odk="http://www.opendatakit.org/xforms">
  <h:head>
    <h:title>209-email</h:title>
    <model>
      <instance>
        <data id="209-email" version="1644197953">
          <meta>
            <instanceID/>
          </meta>
          <email/>
          <text1/>
        </data>
      </instance>
      <itext>
        <translation lang="English">
          <text id="/data/text1:label">
            <value>Text 1 label</value>
          </text>
          <text id="/data/text1:hint">
            <value>Text 1 hint</value>
          </text>
        </translation>
      </itext>
      <bind nodeset="/data/meta/instanceID" type="string" readonly="true()" jr:preload="uid"/>
      <bind nodeset="/data/email" type="string" jr:preload="property" jr:preloadParams="email"/>
      <bind nodeset="/data/text1" type="string"/>
    </model>
  </h:head>
  <h:body>
    <input ref="/data/text1">
      <label ref="jr:itext('/data/text1:label')"/>
      <hint ref="jr:itext('/data/text1:hint')"/>
    </input>
  </h:body>
</h:html>

Filled and submitted: The email set in Collect user metadata (noreply@email.org) shows in the submission.

This shows that at least the happy path works. Who knows any edge cases we should test in addition?