Addition of metric source - replSetGetConfig for getting voting member information

[jaison8940]

Is your feature request related to a problem? Please describe.
There is no metric exposed currently to know whether a node is voting member or not.

E.g.
mongodb_config_members_votes 0 -> non voting member
mongodb_config_members_votes 1 -> voting member

Describe the solution you'd like
I would like to write a new collector for replSetGetConfig.

Describe alternatives you've considered
I could not find any alternatives.

[hiroshi]

Hi, I wrote a patch about adding replsetGetConfig metrics.

• replSetGetConfigCollector #295

This is a forked version based on old version of mongodb_exporter (maybe around 0.20).

It had worked for me so far, but after our MongoDB is upgraded to 5.0, it keep missing $collStats.
(Maybe some compatibility issues between MongoDB versions and the old expoter versions).

I'm going to work around this issue.
However, once I gave up the patch to be merged to main and I am tired of catching up to new code base.

I may share some information when it goes well.