Upgrade the Prometheus client to v1.11.1.
This commit is the result of running:
```
go get github.com/prometheus/client_golang@v1.11.1 \
&& go mod tidy && go mod vendor
```
See https://github.com/prometheus/client_golang/security/advisories/GHSA-cg3q-j54f-5p7p
**What this PR does / why we need it**:
Upgrades `github.com/prometheus/client_golang` to v1.11.1, where the vulnerability has been fixed.
b8cf9c528f