Backport of [NET-8368] security: bump Go version to 1.21.8 into release/1.16.x

[dhiaayachi]

Backport

This PR is auto-generated from hashicorp#20812 to be assessed for backporting due to the inclusion of the label backport/1.16.

The below text is copied from the body of the original PR.

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This bumps go version to 1.21.8.

Description

Resolves multiple CVEs from the latest Go release.
CVE-2024-24783 (crypto/x509).
CVE-2023-45290 (net/http).
CVE-2023-45289 (net/http, net/http/cookiejar).
CVE-2024-24785 (html/template).
CVE-2024-24784 (net/mail).

Resolves Docker Scout scanner vulnerabilities on the Consul Go base image by using alpine3.19
CVE-2023-52425
CVE-2023-52426⁠

Testing & Reproduction steps

make go-build-image

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

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Overview of commits

• d65cacc - 60ab156