fix(flag): incorrect behavior for deprected flag --clear-cache

[afdesk]

Description

ClearCache should be initialized for correct message.

Before:

$ trivy image --clear-cache
Scan a container image
...
2024-07-31T18:13:26+06:00	FATAL	Fatal error	unknown flag: --clear-cache

After:

$ trivy image --clear-cache
2024-07-31T18:14:29+06:00	ERROR	"--clear-cache" was removed. Use "trivy clean --scan-cache" instead
2024-07-31T18:14:29+06:00	FATAL	Fatal error	flag error: cache flag error: unable to parse flag: removed flag ("--clear-cache")

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[afdesk]

@knqyf263 @DmitriyLewen could you take a look at this small fix? thanks

[knqyf263]

@aqua-bot backport release/v0.54

[aqua-bot]

Backport PR created: #7285