Add function to extract and cache CoreDNS Binary in VHD for localdns

[SriHarsha001]

What type of PR is this?
feature

What this PR does / why we need it:
This PR adds a function to extract a coredns binary from cached coredns container images in the VHD. It extracts binary of n-1 coredns image version and latest revision version (v.Major.Minor.Patch-Revision) and copies it to /opt/azure/containers/localdns/binary/coredns path. This binary will be used by localdns systemd unit. The function also handles the cleanup of temporary directories and unmounting of images.

Which issue(s) this PR fixes:

Fixes # None

Requirements:
Build

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Special notes for your reviewer:
Not sure if there is a way to write unit tests for this file.

Release note:

none

[SriHarsha001]

Manually tested both the functions on an AKS agent node.

./testCoreDnsBinaryExtractedAndCached.sh
CoreDnsBinaryExtractedAndCached: Checking for existence of coredns binary at /opt/azure/containers/localdns/binary/coredns
CoreDnsBinaryExtractedAndCached: Expected CoreDNS version (n-1 latest revision): 1.9.4-5
CoreDnsBinaryExtractedAndCached: Verify extracted CoreDNS version: 1.9.4
CoreDnsBinaryExtractedAndCached: Expected version: 1.9.4-5 of coredns binary is extracted and cached at /opt/azure/containers/localdns/binary/coredns

and

./extractAndCacheCoreDnsBinary.sh

cat /opt/azure/vhd-install.complete | grep coredns
  - mcr.microsoft.com/oss/v2/kubernetes/coredns:v1.11.3-6
  - mcr.microsoft.com/oss/v2/kubernetes/coredns:v1.9.4-5
Copied coredns binary of v1.9.4-5 to /opt/azure/containers/localdns/binary/coredns
Successfully copied coredns binary of v1.9.4-5

[github-actions]

No changes to cached containers or packages on Windows VHDs