Allow *.ir.json as alternative IR filename

[gatesn]

This line is strict for *.conjure.json: https://github.com/palantir/gradle-conjure/blob/develop/gradle-conjure/src/main/java/com/palantir/gradle/conjure/ConjureLocalGenerateGenericTask.java#L30

But the Conjure Godel plugin generates *.ir.json files making them unusable: https://github.com/palantir/godel-conjure-plugin/blob/96bccdf6c9de1eec90a94a601a677b0bd2182d39/conjureplugin/publish.go#L65

It may be easier to relax this plugin so it works against all previously published IR files even if we go on to fix the godel plugin too.