fix: Init internal server log along with loki's server instance

[periklis]

What this PR does / why we need it:
Currently Loki's internal server instance is running by default in a panic: nil pointer dereference because along all the updates for 3.0.0, we missed to initialize this server properly:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x84a4ff]

goroutine 1 [running]:
github.com/go-kit/log/level.NewFilter(...)
	/src/loki/vendor/github.com/go-kit/log/level/level.go:43
github.com/grafana/dskit/log.NewGoKitWithLevel({{0x0?, 0xc00192c208?}, 0x0?}, {0x0, 0x0})
	/src/loki/vendor/github.com/grafana/dskit/log/gokit.go:34 +0x21f
github.com/grafana/dskit/server.newServer({{0x0, 0x0}, 0x0, {0x2a68ab9, 0x3}, {0x0, 0x0}, 0xc1d, 0x0, {0x0, ...}, ...}, ...)
	/src/loki/vendor/github.com/grafana/dskit/server/server.go:254 +0x67
github.com/grafana/dskit/server.New({{0x0, 0x0}, 0x0, {0x2a68ab9, 0x3}, {0x0, 0x0}, 0xc1d, 0x0, {0x0, ...}, ...})
	/src/loki/vendor/github.com/grafana/dskit/server/server.go:241 +0x5f
github.com/grafana/loki/v3/pkg/loki.(*Loki).initInternalServer(0xc000d46000)
	/src/loki/pkg/loki/modules.go:213 +0xb8
github.com/grafana/dskit/modules.(*Manager).initModule(0xc000150e40, {0x7ffdd3022ccb, 0xd}, 0x1?, 0xc0008f88d0?)
	/src/loki/vendor/github.com/grafana/dskit/modules/modules.go:136 +0x1f7
github.com/grafana/dskit/modules.(*Manager).InitModuleServices(0x0?, {0xc000e8dca0, 0x1, 0xc0008e8660?})
	/src/loki/vendor/github.com/grafana/dskit/modules/modules.go:108 +0xd8
github.com/grafana/loki/v3/pkg/loki.(*Loki).Run(0xc000d46000, {0x0?, {0x4?, 0x3?, 0x4912940?}})
	/src/loki/pkg/loki/loki.go:453 +0x9d
main.main()
	/src/loki/cmd/loki/main.go:122 +0x113b

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

The internal server in Loki is mainly used in mTLS setups on Kubernetes where we want to allow TLS-secured Readiness/Liveness-Checks without client certificates. Usually k8s readiness/liveness checks do not support mTLS.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[cyriltovena]

LGTM