feat: Add the ability to use a web identity token file (#240)

* feat: Add the ability to use a web identity token file

* mark web identity token file as not required

* fix indentation

* better docs and added support for relative vs absolute paths

* bind sts context and adjust fs calls

* exclude tags if using web identity token file

* fix readme aand adjust tag removal logic

* undo re-ordering of lines

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

action.yml

@@ -34,6 +34,11 @@ inputs:
       environment with the assumed role credentials rather than with the provided
       credentials
     required: false
+  web-identity-token-file:
+    description: >-
+      Use the web identity token file from the provided file system path in order to
+      assume an IAM role using a web identity. E.g., from within an Amazon EKS worker node
+    required: false
   role-duration-seconds:
     description: "Role duration in seconds (default: 6 hours)"
     required: false