Fix BigQuery query template to retrieve training data

[davidheryanto]

Previous BigQuery query template used by DatasetService to retrieve training data has some errors for e.g. it creates query like

# mygcpproject.mydataset.mycolumn is not a valid column name
SELECT mygcpproject.mydataset.mycolumn FROM mygcpproject.mydataset.mycolumn LIMIT 5

This is a fix to the templates.

Extra notes

How to reproduce this error using Feast Python SDK which will call the DatasetService:

Assuming you have ingested feature: myentity.myfeature with event timestamp between 2019-01-01 and 2019-01-02

# Import details are ommitted
# ...

feature_set = FeatureSet(entity="myentity", 
                         features=["myentity.myfeature"])
dataset_info = feast_client.create_dataset(feature_set, "2019-01-01", "2019-01-02")
dataset = fs.download_dataset_to_df(dataset_info, staging_location="gs://mybucket")

[zhilingc]

/lgtm

[pradithya]

/approve

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: pradithya

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [pradithya]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[zhilingc]

/lgtm