[RELEASE-1.11] Move to Golang version 1.21 (#546)

[skonto]

Proposed Changes

• Required for [RELEASE-1.11] [SRVKS-661][Backport] Support http1 full duplex per workload (#14568) #591.
• We need the same for 1.12 but needs to be done manually.
• Afaik we are already building with 1.21.x downstream so it should be safe.

[skonto]

/retest

[ReToCode]

/lgtm
/approve
/hold let's wait until we know that we can productize it with go 1.21

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ReToCode, skonto

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[skonto]

@ReToCode it seems we are ok with the productization https://redhat-internal.slack.com/archives/CF5ANN61F/p1705515999236559

[ReToCode]

👍
/unhold

[ReToCode]

/cherry-pick release-v1.12

[openshift-cherrypick-robot]

@ReToCode: #592 failed to apply on top of branch "release-v1.12":

Applying: Move to Golang version 1.21 (#546)
Using index info to reconstruct a base tree...
M	openshift/performance/patches/perf.patch
Falling back to patching base and 3-way merge...
Auto-merging openshift/performance/patches/perf.patch
CONFLICT (content): Merge conflict in openshift/performance/patches/perf.patch
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Move to Golang version 1.21 (#546)
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherry-pick release-v1.12

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