Add dpm

[RiugaBachi]

The standalone daml-sdk's Daml Assistant got discontinued a while back (not sure which version, but can confirm 3.4.10 is one of them), and was replaced by dpm.

We do have a need for dpm in Obsidian internal projects, so I figured I'd add it here.

As a result of the deprecation, each version spec can now only define either a daml-sdk spec or a dpm spec, so either of these can be nullable and are optionally included in the shell if they are defined. Sample install error for daml-sdk using sdkVersion=3.4.10:

daml: HTTP connection failed
  context: Installing extracted SDK release.
  details: HttpExceptionRequest Request {
  host                 = "api.github.com"
  port                 = 443
  secure               = True
  requestHeaders       = [("Accept","application/vnd.github+json"),("User-Agent","Daml-Assistant/0.0")]
  path                 = "/repos/digital-asset/daml/releases"
  queryString          = "?per_page=100"
  method               = "GET"
  proxy                = Nothing
  rawBody              = False
  redirectCount        = 10
  responseTimeout      = ResponseTimeoutMicro 10000000
  requestVersion       = HTTP/1.1
  proxySecureMode      = ProxySecureWithConnect
}

I haven't looked into whether we can circumvent this to still get a partial install of the daml-sdk using these more recent versions; but I figured we should be moving away from it at these later daml versions anyhow so maybe disabling it is best.

I also bumped the default version to 3.4.10 in anticipation of maybe moving to dpm if nothing else is blocking us, but we can revert this change if necessary.

Notes:

• In the install script from DA, it runs dpm bootstrap. From what I can tell this seems to just pre-install the most recent SDK. But I feel like we can just leave this up to the user after the fact (they can do their own dpm install <sdk_ver> ). Works fine for me without bootstrapping. Happy to re-add it though.

[RiugaBachi]

Not totally sure what the license for this is, just going to assume it's similar to daml-sdk.

[RiugaBachi]

Actually I was able to get daml-sdk to install by extending this conditional:

  extra-args = if version == "2.8.0" || version == "3.4.10" then "--install-with-custom-version ${version}" else "";

Do we still want to support the standalone SDK in these later version that have dpm though?