Update Go version to 1.21.5

[asf-ci-trafficcontrol]

What does this PR (Pull Request) do?

This PR makes the Go components of Traffic Control build using Go version 1.21.5 and updates the golang.org/x/ dependencies.

See the Go 1.21.5 release notes:

go1.21.5 (released 2023-12-05) includes security fixes to the go command, and the net/http and path/filepath packages, as well as bug fixes to the compiler, the go command, the runtime, and the crypto/rand, net, os, and syscall packages. See the Go 1.21.5 milestone on our issue tracker for details.

Which Traffic Control components are affected by this PR?

• Traffic Control Cache Config (t3c, formerly ORT)
• Traffic Control Health Client (tc-health-client)
• Traffic Control Client
• Traffic Monitor
• Traffic Ops
• Traffic Stats
• Grove
• CDN in a Box - Enroller
• CI tests for Go components
• Build system - Go version in builder images

What is the best way to verify this PR?

Run unit tests and API tests. Since this is only a patch-level version update, the only changes were bugfixes. Breaking changes would be unexpected.

The following criteria are ALL met by this PR

• Existing tests are sufficient, no additional tests necessary
• The documentation only mentions the major Go version, no documentation updates necessary.
• The changelog already mentions updating to Go 1.21, no additional changelog message necessary.
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)