Fix snapshotting example build

[pnasrat]

Description of changes:

Updates go mod for 1.21, tc-redirect-tap, and cni plugins

Removes deleted dependency github.com/mitchellh/osext

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

With out this build fails:

$ make
go build -o snapshot-example
mkdir -p bin
GOBIN=/home/pnasrat/workspace/src/github.com/firecracker-microvm/firecracker-go-sdk/examples/cmd/snapshotting/bin go install github.com/awslabs/tc-redirect-tap/cmd/tc-redirect-tap@v0.0.0-20220715050423-f2af44521093
go: github.com/awslabs/tc-redirect-tap/cmd/tc-redirect-tap@v0.0.0-20220715050423-f2af44521093: version constraints conflict:
	github.com/awslabs/tc-redirect-tap@v0.0.0-20220715050423-f2af44521093 indirectly requires github.com/mitchellh/osext@v0.0.0-20151018003038-5e2d6d41470f: github.com/mitchellh/osext@v0.0.0-20151018003038-5e2d6d41470f: invalid version: git ls-remote -q origin in /home/pnasrat/go/pkg/mod/cache/vcs/94ed57c5b21c953d93b47487113db43a5c9b69fd990329ec70dc77348c4dd443: exit status 128:
	fatal: could not read Username for 'https://github.com': terminal prompts disabled
Confirm the import path was entered correctly.
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make: *** [Makefile:47: bin/tc-redirect-tap] Error 1

[swagatbora90]

@pnasrat Thanks for your contribution. Please rebase the PR.

[swagatbora90]

The SDK currently does not define a policy for go version support. Our main intention has been to not break support for those SDK users who are on the LTS version of some of the popular linux distros such as Debian 11, Ubuntu 22.04 LTS. That is the reason why we have kept support for older versions of go. However we have realized that in some cases it becomes necessary to update the go version since newer dependency version no longer support old versions of go (or we end up pinning the version which is less favorable). See #364

[pnasrat]

This was handled in the merge #546 which updates to 1.18 and also ran go mod tidy