Update Go version to 1.21.2

[asf-ci-trafficcontrol]

What does this PR (Pull Request) do?

This PR makes the Go components of Traffic Control build using Go version 1.21.2 and updates the golang.org/x/ dependencies.

See the Go 1.21.2 release notes:

go1.21.2 (released 2023-10-05) includes one security fixes to the cmd/go package, as well as bug fixes to the compiler, the go command, the linker, the runtime, and the runtime/metrics package. See the Go 1.21.2 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 #7831 (50163ba) into master (1c4bcb5) will decrease coverage by 36.71%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             master    #7831       +/-   ##
=============================================
- Coverage     65.65%   28.95%   -36.71%     
  Complexity       98       98               
=============================================
  Files           323      602      +279     
  Lines         12836    77415    +64579     
  Branches        970       90      -880     
=============================================
+ Hits           8427    22412    +13985     
- Misses         4050    52904    +48854     
- Partials        359     2099     +1740     

Flag	Coverage Δ
golib_unit	53.86% <ø> (?)
grove_unit	12.02% <ø> (?)
t3c_unit	5.91% <ø> (?)
traffic_monitor_unit	26.44% <ø> (?)
traffic_ops_integration	69.42% <ø> (ø)
traffic_ops_unit	21.63% <ø> (?)
traffic_portal_v2	?
traffic_stats_unit	10.78% <ø> (?)
unit_tests	25.78% <ø> (-48.60%)	⬇️
v3	57.79% <ø> (ø)
v4	79.18% <ø> (ø)
v5	78.58% <ø> (ø)

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see 516 files with indirect coverage changes

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