Add support for azure arc servers

[Kisbogyi]

This code will enable the azure module to work in Azure arc servers as well, because azure arc servers use a separate url, and method for the challenge/response protocol.
https://learn.microsoft.com/en-us/azure/azure-arc/servers/managed-identity-authentication

[github-actions]

Welcome
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[Kisbogyi]

orward to reviewing your Pull r

👍

[GBBx]

Hi,
Thanks @Kisbogyi , this is a great improvement. I'd love to see it merged.
This change could fix the shellcheck:

      CHALLENGE=$(grep Www "$HTTP_HEADER" | sed 's/Www-Authenticate: Basic realm=//g' | sed 's/[^a-zA-Z0-9\/\.\-]//g')
      _H2="Authorization: Basic $(cat "$CHALLENGE")"

(Also fix a typo.)

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Another thing: the tokens are in "/var/opt/azcmagent/tokens/" and not all users have access to it so acme.sh may need to be run by root for this scenario.