Update instructions and config for required local dotnet version (#8213)

# Description

DE was updated to .net 8 in
radius-project/deployment-engine#394. Similar
version is needed to run control plane locally, updating instructions
and `launch.json` to reflect that as the setup is broken with current
instructions due to version mismatch.

Validated updated config locally.

## Type of change

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Fixes: #issue_number

## Contributor checklist
Please verify that the PR meets the following requirements, where
applicable:

- [N/A] An overview of proposed schema changes is included in a linked
GitHub issue.
- [N/A] A design document PR is created in the [design-notes
repository](https://github.com/radius-project/design-notes/), if new
APIs are being introduced.
- [N/A] If applicable, design document has been reviewed and approved by
Radius maintainers/approvers.
- [N/A] A PR for the [samples
repository](https://github.com/radius-project/samples) is created, if
existing samples are affected by the changes in this PR.
- [N/A] A PR for the [documentation
repository](https://github.com/radius-project/docs) is created, if the
changes in this PR affect the documentation or any user facing updates
are made.
- [N/A] A PR for the [recipes
repository](https://github.com/radius-project/recipes) is created, if
existing recipes are affected by the changes in this PR.

Signed-off-by: Karishma Chawla <[email protected]>

.vscode/launch.json

@@ -65,7 +65,7 @@
       "type": "coreclr",
       "request": "launch",
       "preLaunchTask": "Build Deployment Engine",
-      "program": "${workspaceFolder}/../deployment-engine/src/DeploymentEngine/bin/Debug/net6.0/arm-de.dll",
+      "program": "${workspaceFolder}/../deployment-engine/src/DeploymentEngine/bin/Debug/net8.0/arm-de.dll",
       "args": [],
       "cwd": "${workspaceFolder}/../deployment-engine/src/DeploymentEngine",
       "stopAtEntry": false,

docs/contributing/contributing-code/contributing-code-control-plane/running-controlplane-locally.md

@@ -29,7 +29,7 @@ If you need to manually test APIs you can reach them at the following endpoints
 1. Create a Kubernetes cluster, or set your current context to a cluster you want to use. The debug configuration will use your current cluster for storing data.
 2. Clone the `radius-project/radius` and `radius-project/deployment-engine` repo next to each other.
 3. Run `git submodule update --init` in the `deployment-engine` repo.
-4. Install .NET 6.0 SDK - <https://dotnet.microsoft.com/en-us/download/dotnet/6.0>.
+4. Install .NET 8.0 SDK - <https://dotnet.microsoft.com/en-us/download/dotnet/8.0>.
 5. Install C# VS Code extension - <https://marketplace.visualstudio.com/items?itemName=ms-dotnettools.csharp>.
 6. (Optional) Configure any cloud provider credentials you want to use for developing Radius.
 
@@ -161,7 +161,7 @@ dotnet --list-runtimes
 dotnet --list-sdks
 ```
 
-Make sure you see a `6.0` entry in `--list-runtimes` for `Microsoft.AspNetCore.App` and a `6.0` or newer entry for `--list-sdks`.
+Make sure you see a `8.0` entry in `--list-runtimes` for `Microsoft.AspNetCore.App` and a `8.0` or newer entry for `--list-sdks`.
 
 If you run into issues here, please re-read the prerequisites related to installing .NET.