[8.14](backport #39743) Fix Prometheus metric types parser

[mergify]

Overview

When processing a group of metrics of this format, the metric type variable is set to the latest metric type in the group, even if their types might differ. This happens because the parser thinks this is only 1 metric. This change stores the metric types for each base metric name to avoid this issue.

# HELP nginx_sts_server_bytes_total The request/response bytes
# TYPE nginx_sts_server_bytes_total counter
# HELP nginx_sts_server_connects_total The connects counter
# TYPE nginx_sts_server_connects_total counter
# HELP nginx_sts_server_session_seconds_total The session duration time
# TYPE nginx_sts_server_session_seconds_total counter
# HELP nginx_sts_server_session_seconds The average of session duration time in seconds
# TYPE nginx_sts_server_session_seconds gauge
# HELP nginx_sts_server_session_duration_seconds The histogram of session duration in seconds
# TYPE nginx_sts_server_session_duration_seconds histogram
nginx_sts_server_bytes_total{listen="TCP:8091:127.0.0.1",port="8091",protocol="TCP",direction="in"} 0
nginx_sts_server_bytes_total{listen="TCP:8091:127.0.0.1",port="8091",protocol="TCP",direction="out"} 0
nginx_sts_server_connects_total{listen="TCP:8091:127.0.0.1",port="8091",protocol="TCP",code="1xx"} 0
nginx_sts_server_connects_total{listen="TCP:8091:127.0.0.1",port="8091",protocol="TCP",code="2xx"} 0
nginx_sts_server_connects_total{listen="TCP:8091:127.0.0.1",port="8091",protocol="TCP",code="3xx"} 0
nginx_sts_server_connects_total{listen="TCP:8091:127.0.0.1",port="8091",protocol="TCP",code="4xx"} 0
nginx_sts_server_connects_total{listen="TCP:8091:127.0.0.1",port="8091",protocol="TCP",code="5xx"} 171
nginx_sts_server_connects_total{listen="TCP:8091:127.0.0.1",port="8091",protocol="TCP",code="total"} 171
nginx_sts_server_session_seconds_total{listen="TCP:8091:127.0.0.1",port="8091",protocol="TCP"} 0.016
nginx_sts_server_session_seconds{listen="TCP:8091:127.0.0.1",port="8091",protocol="TCP"} 0.000

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Closes Prometheus parser incorrectly classifies counters as histograms #39705

Use cases

Screenshots

Logs

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This is an automatic backport of pull request #39743 done by [Mergify](https://mergify.com).

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)