feat: add license setting get/put api

[zhongwencool]

Fixes https://emqx.atlassian.net/browse/EMQX-10252

Add /license/setting GET/PUT HTTP API for setting the alarm watermark of license.

Summary

🤖 Generated by Copilot at f03d4d0

This pull request adds a new HTTP API endpoint for getting and updating the license setting of EMQ X. It also refactors the license schema and code to use the hocon schema format and macros, and updates the HTTP API documentation accordingly. The files emqx_license_http_api.erl, emqx_license_schema.erl, emqx_license.erl, emqx_license_schema.hocon, and emqx_license_http_api.hocon are modified.

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