Debian 10 Linux Distribution for 3.x needed

Forking from #1798

~~~
Getting site publishing info...
Creating archive for current directory...
Creating archive for current directory...
Creating archive for current directory...
Permission denied
~~~

This is in a [devcontainer pulling 3.0.2106](https://github.com/microsoft/vscode-dev-containers/blob/master/containers/azure-functions-dotnetcore-3.1/.devcontainer/Dockerfile#L50) via zip-download (not apt-get because it's not yet been published to apt). I was pulling 3.0.2009 and changed to 2106 just now to re-download and test. 2009 works fine with the same d/l & install method.

> @brandonh-msft, is this an official dev container? Could you show me where you are downloading from? Once you download, if you add an executable bit to `gozip` (as shown in earlier comments), the error should go away for now.

https://github.com/microsoft/vscode-dev-containers/blob/master/containers/azure-functions-dotnetcore-3.1/.devcontainer/Dockerfile#L50

This `gozip` step needs to be added to the "[other Linux distros](https://github.com/Azure/azure-functions-core-tools#other-linux-distributions)" documentation on the core tools page, then. This was the method I was using to pull down the 3.x version of core tools while it was unavailable on apt-get. However, as stated earlier **I never had to do this step with the 3.0.2009 version** installed in the same manner so I'm not entirely convinced this is _the_ fix.

> Additionally, we published v3 core-tools in apt-get as `azure-functions-core-tools-3`. The documentation update will follow, but sharing here to unblock you.

I'll change the devcontainer to use the apt-get method with this package name and report back if the problem still exists.

I changed the 3.1 devcontainer to use [the same bit of apt-get install that the 2.1 uses](https://github.com/microsoft/vscode-dev-containers/blob/master/containers/azure-functions-dotnetcore-2.1/.devcontainer/Dockerfile#L35):
```
# Install Azure Functions and Azure CLI
&& echo "deb [arch=amd64] https://packages.microsoft.com/repos/azure-cli/ $(lsb_release -cs) main" > /etc/apt/sources.list.d/azure-cli.list \
&& echo "deb [arch=amd64] https://packages.microsoft.com/repos/microsoft-debian-$(lsb_release -cs)-prod $(lsb_release -cs) main" > /etc/apt/sources.list.d/dotnetdev.list \
&& curl -sL https://packages.microsoft.com/keys/microsoft.asc | (OUT=$(apt-key add - 2>&1) || echo $OUT) \
&& apt-get update \
&& apt-get install -y azure-cli azure-functions-core-tools-3 \
```

but ended up with an error:
```
E: Unable to locate package azure-functions-core-tools-3
```

I noticed none of those `echo` shenanigans are documented on the readme for core tools and also that [the .Net 3.1 container runs on Debian 10](https://hub.docker.com/_/microsoft-dotnet-core-sdk/), while our install instructions only go to Debian 9.

Log shows the following package source hits:
```
[2020-02-26T17:03:03.704Z] [PID 23896] [154901 ms] Hit:1 http://security.debian.org/debian-security buster/updates InRelease
Hit:2 http://deb.debian.org/debian buster InRelease
[2020-02-26T17:03:03.746Z] [PID 23896] [154943 ms] Hit:3 http://deb.debian.org/debian buster-updates InRelease
[2020-02-26T17:03:03.778Z] [PID 23896] [154975 ms]
[2020-02-26T17:03:04.350Z] [PID 23896] [155547 ms] Get:4 https://packages.microsoft.com/repos/azure-cli buster InRelease [29.7 kB]
[2020-02-26T17:03:04.741Z] [PID 23896] [155938 ms] Get:5 https://packages.microsoft.com/repos/microsoft-debian-buster-prod buster InRelease [29.8 kB]
[2020-02-26T17:03:04.925Z] [PID 23896] [156122 ms] Get:6 https://packages.microsoft.com/repos/azure-cli buster/main amd64 Packages [2511 B]
Get:7 https://packages.microsoft.com/repos/azure-cli buster/main all Packages [2261 B]
[2020-02-26T17:03:05.099Z] [PID 23896] [156296 ms] Get:8 https://packages.microsoft.com/repos/microsoft-debian-buster-prod buster/main all Packages [556 B]
[2020-02-26T17:03:05.134Z] [PID 23896] [156331 ms]
Get:9 https://packages.microsoft.com/repos/microsoft-debian-buster-prod buster/main amd64 Packages [27.8 kB]
[2020-02-26T17:03:05.270Z] [PID 23896] [156467 ms] Fetched 92.7 kB in 2s (48.4 kB/s)
```

so if I had to guess we're not publishing for Debian 10.

Compare the Debian 10 .NET 3.1 devcontainer Dockerfile with the Debian 9 installation instructions referenced in the issue, then inspect the core-tools page's “other Linux distributions” section. Verify whether azure-functions-core-tools-3 is available for Debian 10 and document or support the working installation path so the package installs successfully on Debian 10.

Written by the indexing model from the issue text.