[Feature Request] Migrate to .NetCore 6

**Feature Request or Bug**
Feature Request

**Describe the feature request or bug**
.NetCore 3.1 is near EOL and will not get patched to work with libssl3 which is the default library for Ubuntu22.04. .NetCore 3.1 is not installable in the latest ubuntu versions, neither with the ubuntu repositories, nor the microsoft ones.

**To Reproduce**
Steps to reproduce the behavior:
1. Try to install dotnet-sdk-3.1
2. ???
4. No profit!

**Expected behavior**
A framework I can actually install on my machine.

**Screenshots**
```text
❯ sudo apt install dotnet-sdk-3.1
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
dotnet-sdk-3.1 : Depends: dotnet-targeting-pack-3.1 (>= 3.1.0) but it is not installable
Depends: aspnetcore-targeting-pack-3.1 (>= 3.1.10) but it is not installable
E: Unable to correct problems, you have held broken packages.

❯ sudo apt install dotnet-targeting-pack-3.1
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Package dotnet-targeting-pack-3.1 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'dotnet-targeting-pack-3.1' has no installation candidate
```

**Covenant Server Information:**
- OS: `Linux [hostname redacted] 5.15.0-48-generic #54-Ubuntu SMP Fri Aug 26 13:26:29 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux`
- Docker or Native: Native

**Browser Information:**
- Not an issue

**Target Information (System that implant is running on):**
- OS: `Linux [hostname redacted] 5.15.0-48-generic #54-Ubuntu SMP Fri Aug 26 13:26:29 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux`
- Version: just pulled

**Additional context**
https://github.com/dotnet/core/issues/7038