Feature Request: Time-Bounded Log Slicing for /var/log/messages and journald (--since / --until)

Problem Statement

In customer environments where /var/log/messages is unrotated or when -l (additional rotated logs) is enabled, supportconfig can collect gigabytes of irrelevant historical logs for incidents that occurred within a specific time window (e.g., a single day or specific outage timeframe). Current line-count (-I, VAR_OPTION_MSG_LINE_COUNT) and size limits (-X) rely on tail, which only captures the most recent events and risks missing older incidents on busy hosts.

Proposed Solution (Inspired by hb_report)

Introduce time-window log filtering inspired by hb_report's -f/-t mechanism, built with standard core utilities (date, awk, journalctl):

1. CLI / Config Options: Add --since <time> and --until <time> options (avoiding collisions with existing -f / -t directory flags), backed by VAR_OPTION_LOG_FROM_TIME and VAR_OPTION_LOG_TO_TIME in supportconfig.conf.
2. Zero-Dependency Normalization: Use GNU date -d to parse human relative dates ("yesterday", "2 hours ago") and absolute ISO timestamps into Epoch seconds and ISO-8601 strings.
3. High-Performance Syslog Engine: A single-pass awk stream filter that processes both RFC 5424 ISO and legacy BSD timestamps while preserving multi-line stack traces without high memory overhead.
4. Rotated Logs Optimization: Filter messages-*.xz archives by file timestamp before streaming via xzcat | awk, avoiding local disk decompression bloat.
5. Full SLES 12 LTSS to SLES 16 Compatibility: Strictly uses Bash 4.3+, GNU Coreutils, and Awk available across all SLES releases (including SLES 12 SP5 LTSS).

Full Architecture & Implementation Plan

A detailed architectural feasibility study, component breakdown, and phased implementation roadmap is documented here:
https://docs.google.com/document/d/1gPazSN8t-SgPQo41dJqDkFYPev2haJrGd1egyuLiPnI/edit

Start with the linked architectural feasibility study, then trace supportconfig's CLI option handling and supportconfig.conf, including the existing -I, -X, -f and -t options. Review how /var/log/messages, rotated messages-*.xz archives, and journald are currently collected; done means the proposed --since/--until behavior works within the stated SLES compatibility targets.