[suggestion] optionally specify a base profile in add()-method of ConanMultiPackager

[JochenWilhelmyTomTom]

Hi!

I create a ConanMultiPackager and then use .add() to add builds for Linux and Android. All calls to add() assume the same default profile because there is only one call to run() at the end. Therefore it would be a handy feature if add() would take an optional profile parameter, like .add(profile="android", settings={}, ...)

Of course a separate instance of ConanMultiPackager could be created for each profile (and then the profile passed to .run()), but this would conflict a bit with the pagination feature as each instance doesn't see the others.