Enable TLS for /metrics endpoint and add tests

[peppi-lotta]

Description

This PR provides functionality to enable TLS encryption in /metrics endpoint. This a solution can be used as a patch until the TLS solution in the enterprise fork gets upstreamed. There is no timeline for upstreaming hence this PR. The tls can be enables in a similar way as Prometheus metrics are enabled.

Values that can be specified are:

• metricsTLSEnabled
• metricsTLSCACertFile
• metricsTLSCertFile
• metricsTLSPrivateKeyFile
• metricsClientAuthType
• metricsTLSMinVersion

Related issues/PRs

Todos

• Tests
• Documentation
• Release note

Release Note

TBD

Reminder for the reviewer

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