feat(VpcInstanceAuthenticator): add support for new VPC authentication flow (#153)

This commit introduces the VpcInstanceAuthenticator.
This authenticator implements the authentication flow
within a VPC-managed compute resource that is configured to
use the compute resource identity feature.
This involves the use of the compute resource's local
VPC Instance Metadata Service API to retrieve an instance identity
token, and then exchange that token for an IAM access token.
The IAM access token is then used to authenticate outbound REST
API requests by adding an Authorization containing the access token.

Author: padamstx

.secrets.baseline

@@ -3,7 +3,7 @@
     "files": "package-lock.json|^.secrets.baseline$",
     "lines": null
   },
-  "generated_at": "2021-10-05T00:34:30Z",
+  "generated_at": "2021-10-25T15:49:19Z",
   "plugins_used": [
     {
       "name": "AWSKeyDetector"
@@ -67,26 +67,26 @@
   "results": {
     "Authentication.md": [
       {
-        "hashed_secret": "47fcf185ee7e15fe05cae31fbe9e4ebe4a06a40d",
+        "hashed_secret": "91dfd9ddb4198affc5c194cd8ce6d338fde470e2",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 192,
+        "line_number": 71,
         "type": "Secret Keyword",
         "verified_result": null
       },
       {
         "hashed_secret": "98635b2eaa2379f28cd6d72a38299f286b81b459",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 316,
+        "line_number": 404,
         "type": "Secret Keyword",
         "verified_result": null
       },
       {
-        "hashed_secret": "91dfd9ddb4198affc5c194cd8ce6d338fde470e2",
+        "hashed_secret": "47fcf185ee7e15fe05cae31fbe9e4ebe4a06a40d",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 348,
+        "line_number": 439,
         "type": "Secret Keyword",
         "verified_result": null
       }
@@ -104,23 +104,23 @@
         "hashed_secret": "d4c3d66fd0c38547a3c7a4c6bdc29c36911bc030",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 43,
+        "line_number": 44,
         "type": "Secret Keyword",
         "verified_result": null
       },
       {
         "hashed_secret": "8318df9ecda039deac9868adf1944a29a95c7114",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 45,
+        "line_number": 46,
         "type": "Secret Keyword",
         "verified_result": null
       },
       {
         "hashed_secret": "9a66213cc16d178fdbf9f4da6b7bd92497fda404",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 51,
+        "line_number": 52,
         "type": "Secret Keyword",
         "verified_result": null
       }
@@ -196,7 +196,7 @@
         "hashed_secret": "028b5586cf1cd56839aa65b4546373e12fb60396",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 678,
+        "line_number": 706,
         "type": "Secret Keyword",
         "verified_result": null
       }
@@ -248,15 +248,15 @@
         "hashed_secret": "f2e7745f43b0ef0e2c2faf61d6c6a28be2965750",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 71,
+        "line_number": 96,
         "type": "Secret Keyword",
         "verified_result": null
       },
       {
         "hashed_secret": "e4f50034475acff058e17b35679f8ef1e54f86c5",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 85,
+        "line_number": 98,
         "type": "Secret Keyword",
         "verified_result": null
       }