dotnet-install.sh depends on awk without checking for it #746

The minimal Azure Linux 4 base image (mcr.microsoft.com/azurelinux/core:4) does not include awk. dotnet-install.sh only checks for curl or wget, so it accepts this environment but can fail later when resolving a channel/latest version.

The missing dependency surfaced when moving SuperPMI workloads to the Azure Linux 4 Helix image: dotnet/runtime#136337. The image-side fix is dotnet/dotnet-buildtools-prereqs-docker#1782.

awk is used in:

• get_download_link_from_aka_ms: parsing redirect status codes and the download URL (--channel/latest resolution).
• parse_globaljson_file_for_version: parsing the SDK version (--jsonfile).
• get_remote_file_size: extracting Content-Length after a download; failure here can be tolerated.
• downloadcurl / downloadwget: parsing HTTP status codes on download failures.

Explicit --version skips the aka.ms path, so the problem does not necessarily prevent every installation. Please check for awk up front with a clear prerequisite error, or remove the dependency.