fix(rbac): for compatibility with old data schema, extend the existing field as an extra

[lafirest]

Fixes

Summary

🤖 Generated by Copilot at e175c21

Refactor the emqx_app record and the backup and restore logic, and unify the role names for the dashboard and the management API. This reduces code duplication, improves readability, and simplifies the RBAC system.

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
• Added property-based tests for code which performs user input validation
• 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
• Created PR to emqx-docs if documentation update is required, or link to a follow-up jira ticket
• 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

[zmstone]

if the bootstrap file format is documented in emqx-docs, please make sure the newly supported roles are documented.

[zmstone]

update desc here:

emqx/rel/i18n/emqx_mgmt_api_key_schema.hocon

Lines 9 to 13 in a4ab744

	bootstrap_file.desc:
	"""The bootstrap file provides API keys for EMQX.
	EMQX will load these keys on startup to authorize API requests.
	It contains key-value pairs in the format:`api_key:api_secret`.
	Each line specifies an API key and its associated secret."""