refator: unify diff util functions, remove dup implements

[howieyuen]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N

2. What is the scope of this PR (e.g. component or file name):

pkg/util/diff/diff.go
pkg/engine/operation/diff.go
pkg/kusionctl/cmd/diff/options.go

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• refactor diff util implements

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test

6. Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

refatcor pkg/util/diff, support `ToHumanReportString`, `ToRawReportString` and `ToReportString` for both

[coveralls]

Coverage increased (+0.4%) to 73.071% when pulling 40306cf on howieyuen:refactor-diff-util into 182d162 on KusionStack:main.

[elliotxx]

lgtm

[adohe]

overall lgtm