docs: Correct HAProxy configuration in HA Mode docs for pmm v3

[ddkozyreva]

Description

Hi! Your leader health check handle has changed in v3:

POST /v1/leaderHealthCheck --> GET /v1/server/leaderHealthCheck

The documentation (https://pmm-doc.onrender.com/3/install-pmm/HA.html#step-7-set-up-haproxy) still uses the old path. Please correct it.

Now:

http-check send meth POST uri /v1/leaderHealthCheck ver HTTP/1.1 hdr Host www

Need:

http-check send meth GET uri /v1/server/leaderHealthCheck ver HTTP/1.1 hdr Host www

Suggested solution

No response

Additional context

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