Fix/restore dynamodump from backup with gsis

[w0rks74710n]

When trying to restore tables that were generated using the backup functionality of dynamodump, the Table and GSI schema from the describe_table boto3 API call is not fully compatible with the create_table operation of the API. This PR makes sure that the correct payloads are passed to the create_table API call when GSIs are present in the backup data. It also makes sure that when a backup Table is configured in on-demand mode (provisioned throughput set to 0 for all WCU and RCU) the default value of RESTORE_WRITE_CAPACITY is used instead (otherwise the parameter validation of the API will fail).

Without these changes, the output of the process will throw the following error when restoring a table with GSIs:

Traceback (most recent call last):
  File "dynamodump/dynamodump/dynamodump.py", line 1389, in <module>
    main()
  File "dynamodump/dynamodump/dynamodump.py", line 1354, in main
    do_restore(
  File "dynamodump/dynamodump/dynamodump.py", line 831, in do_restore
    dynamo.create_table(
  File "/lib/python3.8/site-packages/botocore/client.py", line 386, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "/lib/python3.8/site-packages/botocore/client.py", line 677, in _make_api_call
    request_dict = self._convert_to_request_dict(
  File "/lib/python3.8/site-packages/botocore/client.py", line 725, in _convert_to_request_dict
    request_dict = self._serializer.serialize_to_request(
  File "/lib/python3.8/site-packages/botocore/validate.py", line 337, in serialize_to_request
    raise ParamValidationError(report=report.generate_report())
botocore.exceptions.ParamValidationError: Parameter validation failed:
Invalid value for parameter ProvisionedThroughput.ReadCapacityUnits, value: 0, valid min value: 1
Unknown parameter in GlobalSecondaryIndexes[0]: "IndexStatus", must be one of: IndexName, KeySchema, Projection, ProvisionedThroughput
Unknown parameter in GlobalSecondaryIndexes[0]: "IndexSizeBytes", must be one of: IndexName, KeySchema, Projection, ProvisionedThroughput
Unknown parameter in GlobalSecondaryIndexes[0]: "ItemCount", must be one of: IndexName, KeySchema, Projection, ProvisionedThroughput
Unknown parameter in GlobalSecondaryIndexes[0]: "IndexArn", must be one of: IndexName, KeySchema, Projection, ProvisionedThroughput
Unknown parameter in GlobalSecondaryIndexes[0].ProvisionedThroughput: "NumberOfDecreasesToday", must be one of: ReadCapacityUnits, WriteCapacityUnits
Invalid value for parameter GlobalSecondaryIndexes[0].ProvisionedThroughput.ReadCapacityUnits, value: 0, valid min value: 1
Unknown parameter in GlobalSecondaryIndexes[1]: "IndexStatus", must be one of: IndexName, KeySchema, Projection, ProvisionedThroughput
Unknown parameter in GlobalSecondaryIndexes[1]: "IndexSizeBytes", must be one of: IndexName, KeySchema, Projection, ProvisionedThroughput
Unknown parameter in GlobalSecondaryIndexes[1]: "ItemCount", must be one of: IndexName, KeySchema, Projection, ProvisionedThroughput
Unknown parameter in GlobalSecondaryIndexes[1]: "IndexArn", must be one of: IndexName, KeySchema, Projection, ProvisionedThroughput
Unknown parameter in GlobalSecondaryIndexes[1].ProvisionedThroughput: "NumberOfDecreasesToday", must be one of: ReadCapacityUnits, WriteCapacityUnits
Invalid value for parameter GlobalSecondaryIndexes[1].ProvisionedThroughput.ReadCapacityUnits, value: 0, valid min value: 1

[w0rks74710n]

Closed in order to fix failing tests first

[bchew]

Thanks for the PR @w0rks74710n