get_runtime_stats.sh - Improve discoverability and specification of grep patterns for common timestamp formats

[power720]

Problem

The --mode timestamp option of get_runtime_stats.sh is capable of calculating runtime from dates in the following formats:

• 2022-01-02 23:45:01
• Sun Jan 2 23:45:01 CST 2022

This is useful for calculating runtime on SETSM jobfiles logs which uses the Sun Jan 2 23:45:01 CST 2022 format. However, the default behavior is hardcoded to the 2022-01-02 23:45:01 format and requires to user to discover and pass the commented out pattern specified in the script to parse the Sun Jan 2 23:45:01 CST 2022 format.

The Sun Jan 2 23:45:01 CST 2022 format grep from line 197:
#timestamp_grep="([A-Z][a-z]+ +[A-Z][a-z]+ +[0-9]+ +[0-9]{2}:[0-9]{2}:[0-9]{2} +[A-Z]+ +[0-9]+)" # 'date' program default format'

Requested Improvement

Add a --timestamp-format option that would assign the correct `--timestamp-grep' value for these common datetime formats.