[Bug] Continuous profiling policy validation: condition doesn't match error message

### Search before asking - [x] I had searched in the [issues](https://github.com/apache/skywalking/issues?q=is%3Aissue) and found no similar issues. ### Apache SkyWalking Component OAP server (apache/skywalking) ### What happened In ContinuousProfilingMutationService.validatePolicyItem(), the validation condition uses < 0 but the error messages say "must bigger than zero". https://github.com/apache/skywalking/blob/9e57d91daae1a7511d1e34584fd573af557364c6/oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/profiling/continuous/ContinuousProfilingMutationService.java#L127-L128 https://github.com/apache/skywalking/blob/9e57d91daae1a7511d1e34584fd573af557364c6/oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/profiling/continuous/ContinuousProfilingMutationService.java#L133-L134 https://github.com/apache/skywalking/blob/9e57d91daae1a7511d1e34584fd573af557364c6/oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/profiling/continuous/ContinuousProfilingMutationService.java#L145-L146 ### What you expected to happen The validation condition should match the error message semantics. There are two possible fixes: Option A - Fix the condition: Change < 0 to <= 0, since a threshold of 0 (e.g., 0 threads, 0 system load) has no practical meaning as a profiling trigger (it would mean "always trigger"). Option B - Fix the message: Change the message to "must be equal to or bigger than zero" (i.e., "must not be negative"), if 0 is intentionally allowed as a valid threshold. I'd like to hear from the maintainers which direction is correct before submitting a PR. ### How to reproduce omit ### Anything else _No response_ ### Are you willing to submit a pull request to fix on your own? - [x] Yes I am willing to submit a pull request on my own! ### Code of Conduct - [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)