This PR changes the way the IPA method is read in the run command for `build ipa` command. If export options plist argument is provided it takes method name from plist, otherwise it uses the method name from export method argument.

*List which issues are fixed by this PR. You must list at least one issue. An issue is not required if the PR fixes something trivial like a typo.*
fixes [#122179](https://github.com/flutter/flutter/issues/122179)