[ts-command-line] Allow more than one character for parameterShortName

[douglasg14b]

Summary

For CLIs with many parameters, 2-letter short-name parameters are often desirable to maintain semantics. Forcing them to only be a single letter forces seemingly confusing short params or no short params at all

For exmaple:

--source-account 
    -sa
--target-account 
    -ta
--source-region 
    -sr
--target-region 
    -tr

Related to the following error:

The parameter short name must be a dash followed by a single upper-case or lower-case letter (e.g. "-a")

Standard questions

Please answer these questions to help us investigate your issue more quickly:

Question	Answer
Package name:	@rushstack/ts-command-line
Package version?	4.23.2
Operating system?	N/A
Would you consider contributing a PR?	Yes
Node.js version (node -v)?	N/A