Extend format of results.xml for docker backend to support meta scores
Updated format adds the <meta> element under which <score> elements are nested for report meta scores:

<testsuites>
    <testsuite>
        <testcase />
        <testcase />
        ...
    </testsuite>
    <testsuite>
        ...
    </testsuite>
    <meta>
        <score id="meta-tests">3</score>
        <score id="max-meta-tests">17</score>
        <score id="Linter Score">1200</score>
        <score id="Hints Needed">3</score>
        <score id="style-checks">17</score>
        <score id="max-code-style-checks">44</score>
    </meta>
</testsuites>

These meta scores will be shown in the output console of WebLab when viewed by course staff with observer role, and for students when program output is exposed (non-default).

Submitted by Elmer van Chastelet on 13 February 2023 at 09:00