Support links to previous build in trends

[msvticket]

When generating a report from results generated by allure-maven the trends lack links to reports for previous builds.

As far as I understand this PR allure-framework/allure2#394 this could be achieved by enriching the executor.json with buildOrder, reportName and reportUrl. This file is populated in https://github.com/allure-framework/allure-maven/blob/master/src/main/java/io/qameta/allure/maven/AllureGenerateMojo.java. I suggest that the values are supplied via the configuration/properties to the plugin. buildOrder could default to the BUILD_NUMBER environment variable, reportName to something generic and reportUrl to a file:// url.

I guess I could add data to executor.json with a separate tool, but that seem quite kludgy to me.