Metrics Advisor Readme and samples issues

[v-xuto]

Section link:
Note: Other section codes in Readme examples have Question 1.

Reason:
1).NameError: name 'os' is not defined.
2).NameError: name 'datatime' is not defined.
3).NameError: name 'DataFeedMissingDataPointFillSettings' is not defined.

Suggestion:
1).Add code: import os
2).Add code: import datetime
3).Add code: from azure.ai.metricsadvisor.models import DataFeedMissingDataPointFillSettings
2.
Section Link:

Suggestion:
Remove import datetime, because not use it in this code snippet.
3.
Section link:

Reason:
if len(alerts) > 0:
TypeError: object of type 'ItemPaged' has no len().

Suggestion:
Update

for result in results:
    print("Alert id: {}".format(result.id))
    print("Create on: {}".format(result.created_on))
return results

to:

tolist = []
for result in results:
    tolist.append(result)
    print("Alert id: {}".format(result.id))
    print("Create on: {}".format(result.created_on))
return tolist

Section link:

Reason:
TypeError: sample_list_alerts_async() missing 1 required positional argument: 'alert_config_id'.

Suggestion:
Update to:
alerts = await sample_list_alerts_async(alert_config.id)
5.
Section link:

Suggestion:
Add async before "def".
6.
Section link:

Suggestion:
1).We should import MetricsAdvisorClient from azure.ai.metricsadvisor.aio.
Update to

    from azure.ai.metricsadvisor import MetricsAdvisorKeyCredential
    from azure.ai.metricsadvisor.aio import MetricsAdvisorClient

2).Update to : result = await client.get_feedback(feedback_id=feedback_id)

@jongio for notification.