[prometheus] revert index mapping changes

[tetianakravchenko]

What does this PR do?

• revert index mapping configuration introduces in this PR - [Prometheus] Add dynamic mapping to fix prometheus histogram type #3891 (reason - issue was fixed)
• add description to the http config options. Context: from https://www.elastic.co/guide/en/beats/metricbeat/current/metricbeat-module-prometheus.html#_example_configuration_51:
  prometheus module supports the options described in Standard HTTP config options
• bump kibana version to 8.4, because mapping fix was added in 8.4

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• [ ]

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• Start Time: 2022-08-24T09:32:37.574+0000

• Duration: 14 min 16 sec

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Name	Metrics % (covered/total)	Diff
Packages	100.0% (0/0)	💚
Files	100.0% (0/0)	💚 2.857
Classes	100.0% (0/0)	💚 2.857
Methods	66.667% (6/9)	👎 -22.655
Lines	100.0% (0/0)	💚 9.141
Conditionals	100.0% (0/0)	💚