`DockerCompose.exec()` that supports stdin

[nedtwigg]

The pg_restore command can take a file argument, or you can pass the file contents over stdin. In order to pass a file, you have to deal with mounting, but over stdin you don't. Right now there's no way to pass content to stdin, and it would be useful if there was.

Maybe add an Optional<byte[]> stdin parameter which would be written to the process stdin?

https://github.com/palantir/docker-compose-rule/blob/c789acc89e818729747b73ef81c2ca22518f67ae/docker-compose-rule-core/src/main/java/com/palantir/docker/compose/execution/DockerComposeExecOption.java#L23-L26