fix: keep percentage type's range is 0%~100%

[zhongwencool]

Fixes https://emqx.atlassian.net/browse/EMQX-10551

1. Keep percentage range is 0%~100%.
2. fix fill_default raw_conf crash when check_process_watermark.

Summary

🤖 Generated by Copilot at 11ee6ab

This pull request adds support for percent values in the configuration schema, and fixes a bug that caused the filter_readonly_config function to crash when the configuration was invalid or incomplete. It modifies the files emqx_schema.erl and emqx_conf_cli.erl.

PR Checklist

Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:

• Added tests for the changes
• Changed lines covered in coverage report
• Change log has been added to changes/(ce|ee)/(feat|perf|fix)-<PR-id>.en.md files
• For internal contributor: there is a jira ticket to track this change
• If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
• Schema changes are backward compatible

Checklist for CI (.github/workflows) changes

• If changed package build workflow, pass this action (manual trigger)
• Change log has been added to changes/ dir for user-facing artifacts update