Update nats_exporter from 0.11.0 to 0.12.0

[prometheus-rpm-bot]

https://github.com/nats-io/prometheus-nats-exporter/releases/tag/v0.12.0
Release notes:

## Changelog
* fc4f5d5 Removing 'make install-tools' from readme
* 44eb8da Merge pull request #236 from nats-io/deps-update
* a067171 Bumping go module versions
* 135f722 Bumping golang image version
* 5ade09a Updating goreleaser config
* 7b70e95 Adding md path ignore. Formatting
* 828a237 Updating badges
* 7a08d8b Moving lint job to coverage workflow
* ac2a994 Debugging golangci-lint
* 96800e4 Updating Github workflows. Fixed some unreachable code. Updated Makefile. Updated go deps
* 57c2cba Adding openssl config for test certs. Replacing certs. Removing test skip.
* fe8c3eb Merge pull request #234 from nats-io/dependabot/docker/cicd/alpine-3.18.2
* 1a76e8d Bump alpine from 3.18.0 to 3.18.2 in /cicd
* 3a05726 Merge pull request #228 from nats-io/dependabot/docker/cicd/alpine-3.18.0
* cb9b983 Bump alpine from 3.17.3 to 3.18.0 in /cicd
* f7e7238 Merge pull request #227 from nats-io/dependabot/docker/cicd/golang-1.20.4-bullseye
* 01395ba Bump golang from 1.20.3-bullseye to 1.20.4-bullseye in /cicd