A modernization pass

[ferhatelmas]

Related to #744, modernize with go 1.17

[ahmetb]

/approve

but the changes are failing netlify, with error:

9:38:45 AM: ────────────────────────────────────────────────────────────────
9:38:45 AM:   1. build.command from netlify.toml                            
9:38:45 AM: ────────────────────────────────────────────────────────────────
9:38:45 AM: ​
9:38:45 AM: $ hugo --buildFuture -b $DEPLOY_PRIME_URL && cd ./functions &&  go build -o api ./server
9:38:45 AM: Building sites …
9:38:45 AM:                    | EN
9:38:45 AM: -------------------+-----
9:38:45 AM:   Pages            | 40
9:38:45 AM:   Paginator pages  |  0
9:38:45 AM:   Non-page files   |  0
9:38:45 AM:   Static files     |  3
9:38:45 AM:   Processed images |  0
9:38:45 AM:   Aliases          |  0
9:38:45 AM:   Sitemaps         |  1
9:38:45 AM:   Cleaned          |  0
9:38:45 AM: Total in 88 ms
9:38:46 AM: # sigs.k8s.io/krew/site/functions/server
9:38:46 AM: server/main.go:225:12: undefined: io.ReadAll
9:38:46 AM: note: module requires Go 1.15
9:38:46 AM: ​
9:38:46 AM: ────────────────────────────────────────────────────────────────
9:38:46 AM:   "build.command" failed                                        
9:38:46 AM: ────────────────────────────────────────────────────────────────

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahmetb, ferhatelmas

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[ferhatelmas]

@ahmetb PTAL

[ahmetb]

/lgtm
thanks