Add openmetrics format parser

[ide-rea]

This PR is for prometheus/prometheus#8932. After think about the issue, my solution is divide into two steps.

1. Use the openMetricsParser located in https://github.com/prometheus/prometheus/tree/main/pkg/textparse to parse the text exchange format into the MetricFamily map . this step is implemented in this PR.
2. Use https://github.com/prometheus/client_golang/blob/master/prometheus/testutil/promlint/promlint.go promlint to check the metric foramt. If the first step is correct, i'll fastly plan to implement this.

My concern is that, firstly as the openMetricsParser is located in github.com/prometheus/prometheus/ , there may be some hidden circular import problem, although i have tested it works. Secondly, I may be totally wrong about the right direction for solving this issue. i'm very happy to hear from any advices:)!