[Prometheus Receiver] Add test to validate Honor timestamps configuration

[PaurushGarg]

Is your feature request related to a problem? Please describe.
Add a new Prometheus Receiver test to ensure honor_timestamps configurations are honored. honor_timestamps controls whether Prometheus respects the timestamps present in scraped data.

The honor_timestamps is a boolean that can be set to “true” or “false” inside scrape_configs of Prometheus Receiver configuration in OTEL collector configuration yaml file.
[ honor_timestamps: <boolean> | default = true ]

If honor_timestamps is set to “true”, then the timestamps of the metrics exposed by the target will be used. If honor_timestamps is set to “false”, then the timestamps of the metrics exposed by the target will be ignored.

Describe the solution you'd like
We propose the following solution:
To test if the Prometheus receiver handles honor_timestamps configuration, we can configure the Prometheus receiver to scrape testdata and validate the output from the Prometheus receiver.

TestCase 1:

• Set honor_timestamps : true inside scrape_configs of Prometheus Receiver configuration.
• Provide timestamps with the metric in the testdata.
  For Example:

const honorTimestampsPage1 = `
# HELP go_threads Number of OS threads created
# TYPE go_thread gauge
go_threads 19 1634616931195
#EOF`

• Validate that the honor_timestamps were handled and the start_timestamp present in the transformed OTLP data by the Prometheus Receiver contains the same input timestamp given in the testdata.

TestCase 2:

• Set honor_timestamps : false inside scrape_configs of Prometheus Receiver configuration.
• Provide timestamps with the metric in the testdata.
  For Example:

const honorTimestampsPage1 = `
# HELP go_threads Number of OS threads created
# TYPE go_thread gauge
go_threads 19 1634616931195
#EOF`

• Validate that the honor_timestamps were handled and the start_timestamp present in the transformed OTLP data by the Prometheus Receiver contains the scrape start time and not the input timestamp given in the testdata.

Additional context
Related to open-telemetry/wg-prometheus#57
cc: @alolita @Aneurysm9

[PaurushGarg]

@alolita please assign this issue to me. I would like to work on this one.

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