Fix param parsing on --sast-excluded-paths and --ignored-dirs

What does this MR do?

Fixes a bug caused by naive param parsing introduced in !103 (merged):

• --sast-excluded-paths is handled with more care, trimming white space and skipping empty strings;
• --ignored-dirs is handled natively by StringSlice() of urfave/cli, since it is decleard as that type by gitlab.com/gitlab-org/security-products/analyzers/common

Also, this MR replaces !106 (merged) .

What are the relevant issue numbers?

• https://gitlab.com/gitlab-jh/gitlab-jh-enablement/-/issues/325+
• Jihu's issue(Chinese): https://jihulab.com/gitlab-cn/gitlab/-/issues/2978

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests updated/added for this feature/bug
• Job definition updated, if necessary
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• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer