Add iceberg.partition.spec

[hasyimibhar]

PartitionSpec is already implemented here:

tiered-storage-for-apache-kafka/core/src/main/java/io/aiven/kafka/tieredstorage/iceberg/data/SchemaUtils.java

Lines 158 to 205 in cc39369

	static PartitionSpec createPartitionSpec(
	final org.apache.iceberg.Schema schema, final List<String> partitionBy) {
	if (partitionBy.isEmpty()) {
	return PartitionSpec.unpartitioned();
	}
	final PartitionSpec.Builder specBuilder = PartitionSpec.builderFor(schema);
	partitionBy.forEach(
	partitionField -> {
	final Matcher matcher = TRANSFORM_REGEX.matcher(partitionField);
	if (matcher.matches()) {
	final String transform = matcher.group(1);
	switch (transform) {
	case "year":
	case "years":
	specBuilder.year(matcher.group(2));
	break;
	case "month":
	case "months":
	specBuilder.month(matcher.group(2));
	break;
	case "day":
	case "days":
	specBuilder.day(matcher.group(2));
	break;
	case "hour":
	case "hours":
	specBuilder.hour(matcher.group(2));
	break;
	case "bucket": {
	final Pair<String, Integer> args = transformArgPair(matcher.group(2));
	specBuilder.bucket(args.first(), args.second());
	break;
	}
	case "truncate": {
	final Pair<String, Integer> args = transformArgPair(matcher.group(2));
	specBuilder.truncate(args.first(), args.second());
	break;
	}
	default:
	throw new UnsupportedOperationException("Unsupported transform: " + transform);
	}
	} else {
	specBuilder.identity(partitionField);
	}
	});
	return specBuilder.build();
	}

This PR simply adds iceberg.partition.spec, pass it to createPartitionSpec, then pass the partition spec to catalog. createTable.

TBD