Rename docs/example file for http metrics from "http.py" to "http_metrics" as it leads to namespace conflicts in request library

[pavankrish123]

Description

This is a minor fix for a small issue from PR #1116. The example file for demonstrating http metrics is named as http.py. This leads to a shadow import with another file in requests causing the import scream.

(env) basic_meter $ python http.py 
Traceback (most recent call last):
  File "http.py", line 19, in <module>
    import requests
  File "/Users/pavankri/ot/opentelemetry-python/env/lib/python3.8/site-packages/requests/__init__.py", line 43, in <module>
    import urllib3
  File "/Users/pavankri/ot/opentelemetry-python/env/lib/python3.8/site-packages/urllib3/__init__.py", line 7, in <module>
    from .connectionpool import HTTPConnectionPool, HTTPSConnectionPool, connection_from_url
  File "/Users/pavankri/ot/opentelemetry-python/env/lib/python3.8/site-packages/urllib3/connectionpool.py", line 11, in <module>
    from .exceptions import (
  File "/Users/pavankri/ot/opentelemetry-python/env/lib/python3.8/site-packages/urllib3/exceptions.py", line 2, in <module>
    from .packages.six.moves.http_client import IncompleteRead as httplib_IncompleteRead
  File "/Users/pavankri/ot/opentelemetry-python/env/lib/python3.8/site-packages/urllib3/packages/six.py", line 199, in load_module
    mod = mod._resolve()
  File "/Users/pavankri/ot/opentelemetry-python/env/lib/python3.8/site-packages/urllib3/packages/six.py", line 113, in _resolve
    return _import_module(self.mod)
  File "/Users/pavankri/ot/opentelemetry-python/env/lib/python3.8/site-packages/urllib3/packages/six.py", line 82, in _import_module
    __import__(name)
  File "/Users/pavankri/ot/opentelemetry-python/docs/examples/basic_meter/http.py", line 22, in <module>
    from opentelemetry.instrumentation.requests import RequestsInstrumentor
  File "/Users/pavankri/ot/opentelemetry-python/env/lib/python3.8/site-packages/opentelemetry/instrumentation/requests/__init__.py", line 39, in <module>
    from requests import Timeout, URLRequired
ImportError: cannot import name 'Timeout' from partially initialized module 'requests' (most likely due to a circular import) (/Users/pavankri/ot/opentelemetry-python/env/lib/python3.8/site-packages/requests/__init__.py)

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Renamed the file to something appropriate http_metrics.py and that resolved the issue. Verified the example is working as expected

• [ X] Test A

(env) basic_meter   $ mv http.py http_metrics.py
(env) basic_meter   $ python http_metrics.py 
...
ConsoleMetricsExporter(data="ValueRecorder(name="http.client.duration", description="measures the duration of the outbound HTTP request")", labels="(('http.flavor', '1.1'), ('http.method', 'GET'), ('http.status_code', '200'), ('http.url', 'http://example.com'))", value=minmaxsumcount(min=77.86989212036133, max=77.86989212036133, sum=77.86989212036133, count=1), resource={'telemetry.sdk.language': 'python', 'telemetry.sdk.name': 'opentelemetry', 'telemetry.sdk.version': '0.15.dev0'})

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated (N/A)
• Unit tests have been added (N/A)
• Documentation has been updated

[codeboten]

Thanks for the PR!