fix: CLI commands may be terminated with semicolon+whitespace (MINOR)

[vcrfxia]

Description

CLI-specific commands (including run script) may be optionally terminated with a semicolon. However, the KSQL CLI doesn't currently support trailing whitespace for CLI-specific commands terminated with a semicolon, which leads to confusing behavior in some of our demos, as many of them include run script commands terminated with semicolons and newlines. For example:

ksql> RUN SCRIPT '/usr/share/doc/clickstream/clickstream-schema.sql';

(with a new line at the end) results in

Failed to read file: /usr/share/doc/clickstream/clickstream-schema.sql;
Caused by: /usr/share/doc/clickstream/clickstream-schema.sql;

since the presence of the newline causes the semicolon to fail to be stripped, and it gets attached to the end of the filename argument as a result.

This PR fixes the confusing behavior.

Testing done

Unit test + manual.

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[big-andy-coates]

Thanks @vcrfxia - LGTM!