Allow users to set the maximum attachment size in the /unpack resource of tika-server

Adding the option to override the maximum bytes that Unrar parser can handle

so I would not get the TikaMemoryLimitException.

Wish to have the configuration to look like this:

<parser class="org.apache.tika.parser.pkg.UnrarParser">
            <params>
                <param name="byteArrayMaxOverride" type="int">1000000000</param>
            </params>

</parser>