Add php-dom and php-xml to prerequisites (and the Docker image Dockerfile)

[nielsdrost7]

Current Behavior

From the forum:

Installed invoiceplane for a friend ran into a problem that through the customer porthole when viewing the invoice if you want to download the pdf you get an error I needed to install php81-xml and php81-dom to get this to work once again don’t know if all distros are the same but maybe should be noted in the requirement section on the Wiki

Possible Implementation

RUN install-php-extensions \
    bcmath \
    exif \
    gd \
    imagick \
    imap \
dom \ <<<====
xml \ <<<===
    intl \
    mysqli \
    pdo_mysql \
    redis \
    soap \
    xdebug \
    xsl \
    zip

And it's not in the requirements: [wiki/en/1_6/getting_started/requirements.blade.php](https://github.com/InvoicePlane/Wiki/blob/master/wiki/en/1_6/getting_started/requirements.blade.php)