feat: add paginator for opensearch

[digglife]

With this change, we can use paginator for the OpenSearch APIs with Max Results limit, instead of looping with NextToken manually.

# a trivial example
instances = []
opensearch = boto3.client('opensearch')
paginator = opensearch.get_paginator('describe_reserved_instances')
for page in paginator.paginate():
    instances.extend(page['ReservedInstances'])

fixes: #3245

[tim-finnigan]

Thanks for creating this PR, but we can't accept these changes for reasons described in #3245 (comment)