Update Go version to 1.17

[zrhoffman]

This PR

• Makes the Is it time to update Go? GHA workflow update GO_VERSION before setting up the Go version specified in GO_VERSION
• Makes the build-rpms GHA build the ATC builder images if the GO_VERSION has changed in the scope of the PR, or in the last commit if it's not being run on a PR
• Updates the Go version to 1.17 and updates the golang.org/x/ dependencies.

See the Go 1.17 release notes for details.

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Which Traffic Control components are affected by this PR?

• CDN in a Box - Enroller
• Grove
• Traffic Control Client (Go)
• Traffic Monitor
• Traffic Ops
• Traffic Ops ORT
• Traffic Stats
• CI tests for Go components

What is the best way to verify this PR?

Run unit tests and API tests

PR submission checklist

• Existing tests are sufficient
• The documentation pulls the Go version from GO_VERSION, no other documentation changes are necessary
• This PR has a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[zrhoffman]

Rebased to fix the changelog merge conflict

[ocket8888]

t3c failure looks related to this PR and not spurious:

go: go.mod file not found in current directory or any parent directory; see 'go help modules'

[zrhoffman]

t3c failure looks related to this PR and not spurious:

go: go.mod file not found in current directory or any parent directory; see 'go help modules'

That error always happened because go mod vendor was run before cding into the ATC directory. Once in the ATC directory, go get ./... was run instead (changed to go mod vendor in 516df79).

As reported in golang/go#45609, go mod reports no dependencies in symlinked directories, resulting in go mod vendor emptying out the vendor directory. Resolving the symlink when cding into the ATC directory in c931a5f.

[zrhoffman]

Okay, the logic for whether to build or pull the builder images is working.

[zrhoffman]

Now it's actually working.

[ocket8888]

This all LGTM - I'll leave it open for a bit in case you take my advice and remove the double-documented typing, but if not I'll merge it anyway; it's not hurting anything.