Backport of Upgrade to go 1.21.8 into release/1.2.x (#3751)

* backport of commit a860f16

* backport of commit 8174632

---------

Co-authored-by: Chris S. Kim <ckim@hashicorp.com>

.changelog/3741.txt

@@ -0,0 +1,14 @@
+```release-note:security
+Upgrade to use Go `1.21.8`. This resolves CVEs
+[CVE-2024-24783](https://nvd.nist.gov/vuln/detail/CVE-2024-24783) (`crypto/x509`).
+[CVE-2023-45290](https://nvd.nist.gov/vuln/detail/CVE-2023-45290) (`net/http`).
+[CVE-2023-45289](https://nvd.nist.gov/vuln/detail/CVE-2023-45289) (`net/http`, `net/http/cookiejar`).
+[CVE-2024-24785](https://nvd.nist.gov/vuln/detail/CVE-2024-24785) (`html/template`).
+[CVE-2024-24784](https://nvd.nist.gov/vuln/detail/CVE-2024-24784) (`net/mail`).
+```
+
+```release-note:security
+Update the Consul Build Go base image to `alpine3.19`. This resolves CVEs
+[CVE-2023-52425](https://nvd.nist.gov/vuln/detail/CVE-2023-52425)
+[CVE-2023-52426⁠](https://nvd.nist.gov/vuln/detail/CVE-2023-52426)
+```

.go-version

@@ -1 +1 @@
-1.21.7
+1.21.8

control-plane/Dockerfile

@@ -17,7 +17,7 @@
 # go-discover builds the discover binary (which we don't currently publish
 # either).
 ARG GOLANG_VERSION
-FROM golang:${GOLANG_VERSION}-alpine as go-discover
+FROM golang:${GOLANG_VERSION}-alpine3.19 as go-discover
 RUN CGO_ENABLED=0 go install github.com/hashicorp/go-discover/cmd/discover@214571b6a5309addf3db7775f4ee8cf4d264fd5f
 
 # dev copies the binary from a local build