[FEATURE] Add support for AWS Sigv4 request signer

[VachaShah]

Add support for signed requests via AWS sigv4.

[hanopensearch]

@VachaShah Support for AWS Sigv4 reqeust signer in opensearch-py is done in opensearch-project/opensearch-py#133. opensearch-dsl-py uses OpenSearch in opensearch-py for user authentication. Below code shows how it works:

from opensearch_dsl import Search
from opensearchpy import OpenSearch, RequestsHttpConnection, AWSV4SignerAuth
import boto3
import os

# cluster endpoint, for example: my-test-domain.us-east-1.es.amazonaws.com
host = os.getenv('host')
region = 'us-west-2' # e.g. us-west-1
credentials = boto3.Session().get_credentials()
auth = AWSV4SignerAuth(credentials, region)

client = OpenSearch(
    hosts = [{'host': host, 'port': 443}],
    http_auth = auth,
    use_ssl = True,
    verify_certs = True,
    connection_class = RequestsHttpConnection
)

index_name = 'my-dsl-index'

response = client.indices.create(index_name)
print('\nCreating index:')
print(response)

# Add a document to the index.
document = {
  'title': 'python',
  'description': 'beta',
  'category': 'search'
}
id = '1'

response = client.index(
    index = index_name,
    body = document,
    id = id,
    refresh = True
)

print('\nAdding document:')
print(response)

# Search for the document.
s = Search(using=client, index=index_name) \
    .filter("term", category="search") \
    .query("match", title="python")

response = s.execute()

print('\nSearch results:')
for hit in response:
    print(hit.meta.score, hit.title)

# Delete the document.
print('\nDeleting document:')
print(response)

# Delete the index.
response = client.indices.delete(
    index = index_name
)

print('\nDeleting index:')
print(response)

Here is the output:

Creating index:
{'acknowledged': True, 'shards_acknowledged': True, 'index': 'my-dsl-index'}

Adding document:
{'_index': 'my-dsl-index', '_type': '_doc', '_id': '1', '_version': 1, 'result': 'created', 'forced_refresh': True, '_shards': {'total': 2, 'successful': 1, 'failed': 0}, '_seq_no': 0, '_primary_term': 1}

Search results:
0.2876821 python

Deleting document:
<Response: [<Hit(my-dsl-index/1): {'title': 'python', 'description': 'beta', 'category': 'sear...}>]>

Deleting index:
{'acknowledged': True}

[VachaShah]

@hanopensearch That is awesome! Thank you very much for sharing this example. Would love a PR for adding this example in the USER_GUIDE.

[hanopensearch]

@VachaShah here is the PR #65.

[wbeckler]

I would suggest we close this issue given that the feature exists and all that remains is documenting, which is tracked in a separate issue.