Make azd to follow one only convention for environment variables.
azd should use a prefix to avoid any collision with system variables.

azd is currently using environment variables in the form of:

• AZD_XXXX_XXXX... , like:

  • AZD_SKIP_UPDATE_CHECK
  • AZD_DEBUG_FORCE_NO_TTY
  • AZD_FUNC_TEST

• AZURE_DEV_XXXX_XXX..., like:

  • AZURE_DEV_COLLECT_TELEMETRY
  • AZURE_DEV_CI_OS
  • AZURE_DEV_USER_AGENT

• AZURE_XXX..., like:

  • AZURE_ENV_NAME

• XXX..., like: (this should be fixed as could potentially collision)

  • GITHUB_ACTIONS
  • NO_COLOR
  • CODESPACES
  • REMOTE_CONTAINERS

Extra note: azd should also define if setting env vars with empty value is equivalent to adding any value to it.
For example, for bool vars like NO_COLOR, is setting NO_COLOR= the same as NO_COLOR=1? or is the same as not setting the env var.