Update Go version to 1.21.4

[asf-ci-trafficcontrol]

What does this PR (Pull Request) do?

This PR makes the Go components of Traffic Control build using Go version 1.21.4 and updates the golang.org/x/ dependencies.

See the Go 1.21.4 release notes:

go1.21.4 (released 2023-11-07) includes security fixes to the path/filepath package, as well as bug fixes to the linker, the runtime, the compiler, and the go/types, net/http, and runtime/cgo packages. See the Go 1.21.4 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)

[codecov]

Codecov Report

Merging #7859 (cc7ba93) into master (23e9248) will decrease coverage by 2.90%.
Report is 39 commits behind head on master.
The diff coverage is 33.33%.

@@             Coverage Diff              @@
##             master    #7859      +/-   ##
============================================
- Coverage     31.87%   28.97%   -2.90%     
  Complexity       98       98              
============================================
  Files           717      602     -115     
  Lines         82756    77415    -5341     
  Branches        970       90     -880     
============================================
- Hits          26377    22432    -3945     
+ Misses        54218    52889    -1329     
+ Partials       2161     2094      -67     

Flag	Coverage Δ
golib_unit	53.86% <33.33%> (+0.28%)	⬆️
grove_unit	12.02% <ø> (ø)
t3c_unit	5.91% <ø> (ø)
traffic_monitor_unit	26.44% <ø> (ø)
traffic_ops_integration	69.42% <ø> (ø)
traffic_ops_unit	21.68% <ø> (ø)
traffic_portal_v2	?
traffic_stats_unit	10.78% <ø> (ø)
unit_tests	25.81% <33.33%> (-3.39%)	⬇️
v3	57.79% <ø> (ø)
v4	79.18% <ø> (ø)
v5	78.58% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
cache-config/t3c-apply/config/config.go	0.00% <ø> (ø)
cache-config/t3c-apply/torequest/cmd.go	0.00% <ø> (ø)
cache-config/t3c-apply/torequest/torequest.go	5.65% <ø> (ø)
cache-config/t3c-apply/util/gitutil.go	0.00% <ø> (ø)
cache-config/t3c-apply/util/util.go	0.00% <ø> (ø)
cache-config/t3c-check-refs/config/config.go	0.00% <ø> (ø)
cache-config/t3c-check-refs/t3c-check-refs.go	1.78% <ø> (ø)
cache-config/t3c-generate/cfgfile/all.go	51.38% <ø> (ø)
cache-config/t3c-generate/cfgfile/routing.go	84.00% <ø> (ø)
cache-config/t3c-generate/cfgfile/sslkeys.go	0.00% <ø> (ø)
... and 64 more

... and 150 files with indirect coverage changes

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