dotnet lambda package is not reproducible

### Describe the bug

Because `dotnet lambda package` does not zero out the mtimes of the files in the zip, the zip file itself constantly changes on every build. This means that even rerunning a build of the same exact commit will lead to a cdk diff.

### Expected Behavior

`dotnet lambda package` should produce identical results given identical inputs.

### Current Behavior

The original mtimes are preserved, so there is always a diff.

### Reproduction Steps

1. Run `dotnet lambda package`.
2. Use `cdk deploy` to deploy a stack with that lambda function.
3. Run `dotnet lambda package` again.
4. Run `cdk diff`.

### Possible Solution

Set all mtimes to zero (or provide a flag for this).

### Additional Information/Context

_No response_

### Targeted .NET platform

.NET Core 3.1

### CLI extension version

amazon.lambda.tools 4.0.0 dotnet-lambda

### Environment details (OS name and version, etc.)

Debian