utils/golden: support diff of Prometheus Metrics from api server

[Choraden]

This patch adds support of reading, parsing and comparing prometheus metrics from http server.

[what-the-diff]

PR Summary

• Expanded capabilities of utils/golden/prometheus.go module
  The additions to this section of code are focused on enhancing data gathering and parsing related to Prometheus metrics. These changes should boost the flexibility and efficiency of dealing with data from various sources.

• Integration of key libraries
  This update includes the integration of several critical libraries (io, net/http, net/url, and time). This collaboration expands the toolset our software can use, improving its ability to handle various tasks - like better network communication, working with URLs, and managing time-related tasks.

• Addition of the function DiffPrometheusMetricsHTTP
  An agile new feature, it takes a URL and additional filters to refine the scope of data collection. This function fetches data from the specified URL allowing our software to interact and pull data from external web resources more effectively.

• Introduction of parseMetricFamilies function
  A new parsing function was developed specifically to handle Prometheus metric families' data. By adding this function, data culled from Prometheus can be analyzed and classified more efficiently inside our software.

• Inclusion of gatherer struct and its methods
  The 'gatherer' structure and its functionalities are introduced in this pull request. It's designed to wrap the parsed 'metric families' data. This extra layer of functionality enables us to manage, organize, and access our parsed data better. Notably, the gatherer.Gather method returns the encapsulated data, promoting simplified access and usage of processed information.