Add "sam" script for bash on windows

### Describe your idea/feature/enhancement

When using gitbash, on windows we are unable to run the command "sam"

### Proposal

In the "C:\Program Files\Amazon\AWSSAMCLI\bin" folder, I suggest adding a new file called "sam" (no extension) with the following content:

```
DIR="$(dirname "${BASH_SOURCE[0]}")" # get the directory name
"$DIR/../runtime/python.exe" -m samcli "$@"
```