add ProxySQL_Uptime status. It is ProxySQL running time (unit: seconds)

[taylor840326]

Sometimes I want to get some metrics:
for example:

the number of Client_Connections_created per second
the number of Client_Connections_aborted per second
, etc.

But "show mysql status" command only output total number.
So. I add this “ProxySQL_Uptime” metrics.

[renecannao]

Lei,
Thank you for the PR.
Although, I will close this PR and implement it in a different way.
A bit more context on why I will implement differently:

• the information is already available here : it only needs to be made available in SHOW MYSQL STATUS
• time() is not safe: if someone change the clock of the system, the result will be incorrect. This is why the current solution already uses monotonic time.

Thanks

[taylor840326]

@renecannao
👍 OK! 🌹

[renecannao]

Feature introduce in both 1.3.5 and 1.4.0 , both to be released