Support reading the credentials from the ~/.aws/credentials file within the Spark cluster

[julienrf]

Currently, the users of the migrator have to provide their AWS credentials through the config.yaml file. According to the description of #122, in some cases it is desirable to also read the AWS credentials from the user profile (~/.aws/credentials).

This PR addresses this need by using a capability of the Hadoop connector to set a custom AWS credentials provider. We set it to com.amazonaws.auth.profile.ProfileCredentialsProvider, which is the standard profile credentials provider from the AWS SDK.

Ultimately, if necessary we could make this configurable and allow our users to supply which credentials provider to use. This would give them full control on that.

According to #122 (comment), this PR fixes #122.

[julienrf]

After a second thought, I wonder if we should also support reading credentials from environment variables (see also awslabs/emr-dynamodb-connector#185).

[tarzanek]

ideal way is to read from everywhere with some order of preference (and stick to spark ways https://spark.apache.org/docs/latest/configuration.html#dynamically-loading-spark-properties or similar with pre-defined hierarchy and inheritance)

[tarzanek]

@julienrf just fix the commit message - add a reference to
#122
(but don't close it)

I'd like to merge this to fix the credentials to the ones provided by config.yaml

Then in later PRs we can tackle env or assumed role approaches for DynamoDB access

[tarzanek]

merged by 00412dc
closing