RedisIO non-prefix read operations

Read operation in RedisIO is for prefix based look ups. While this can be used for exact key matches as well, the number of operations limits the through put of the function.
I suggest exposing current readAll operation as readbyprefix and using more simpler operations for readAll functionality.
ex:

String output = jedis.get(element);
if (output != null) {
    processContext.output(KV.of(element, output));
}

instead of:
https://github.com/apache/beam/blob/7d240c0bb171af6868f1a6e95196c9dcfc9ac640/sdks/java/io/redis/src/main/java/org/apache/beam/sdk/io/redis/RedisIO.java#L292