[pmm-agent] Get proxysql info using builtin prometheus exporter info

[bmm-alc]

Description

the proxysql-exporter project was not updated for a long time, so likely not maintained anymore (README says it support version 1.2 and 1.3 ...), further more now proxysql has a builtin exporter. (as explained on (/sysown/proxysql/issues/4820#issuecomment-2639719108)

Suggested solution

No response

Additional context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[BupycHuk]

Hi, we were thinking about migrating to built-in prometheus exporter for ProxySQL, but at the moment we don't have enough resources to work on it. You can add it as external exporter to be able to monitor it.