io_properties: fix --update-aws-params and add RunByUser tagging

[fruch]

Summary

Fix the --update-aws-params flag in get_scylla_io_properties.py to produce minimal, correct diffs when updating instance IO parameters.

Changes

Sort aws_io_params.yaml for stable diffs

• Sort instance types by family (letter prefix, generation number, suffix) then by size within each family
• Standardize sub-key ordering to alphabetical (read_bandwidth, read_iops, write_bandwidth, write_iops)
• Ensures updating a single instance type won't cause unrelated diff noise

Add RunByUser tag to EC2 instances

• Add get_username() to identify who launched the instance (matches scylla-cluster-tests pattern)
• Tag all launched instances with RunByUser for cost tracking and ownership
• Add missing import getpass and import subprocess

Fix --update-aws-params to write correct format

• update_single_instance_params was storing the raw io_properties.yaml structure (with disks list wrapper and mountpoint) instead of the flat 4-value format
• update_aws_params_yaml was re-reading/re-writing the entire file per instance in a loop with sort_keys=False
• Both functions produced diffs on unrelated entries when updating a single instance type
• Add extract_io_params() to consistently extract just the 4 IO values
• Add write_aws_params_yaml() using sort_aws_instance_types for consistent ordering
• Remove unused sort_instances_by_size function