bump: go 1.19.5 -> 1.20.1

This PR bumps go to 1.20.1 (https://go.dev/doc/go1.20) which
addresses the following vulnerabilities:
https://pkg.go.dev/vuln/GO-2023-1571
https://pkg.go.dev/vuln/GO-2023-1570
https://pkg.go.dev/vuln/GO-2023-1568

As part of the migration, general Golang
stdlib deprecations and test failures were addressed as well.
Some of those changes are:

* Bump golangci-lint for support with go1.20
* Migrate rand.Seed() calls to the newer rand.New(rand.NewSource(seed))

Co-authored-by: Stephan Renatus <stephan@styra.com>
Co-authored-by: Philip Conrad <philipaconrad@gmail.com>

Signed-off-by: Ashutosh Narkar <anarkar4387@gmail.com>