Conversation JS HTTP Quickstart

[ConstantinChirila]

Description

Added the missing quickstart for how to use the Dapr Conversation with Javascript through the standard HTTP fetch.

Issue reference

#1107

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• The quickstart code compiles correctly
• You've tested new builds of the quickstart if you changed quickstart code
• You've updated the quickstart's README if necessary
• If you have changed the steps for a quickstart be sure that you have updated the automated validation accordingly. All of our quickstarts have annotations that allow them to be executed automatically as code. For more information see mechanical-markdown. For user guide with examples see Examples.

[alicejgibbons]

small changes

[alicejgibbons]

thanks!