Add support for configuring custom certificates via component parameters

[simu]

This PR introduces new component parameters secrets and cert_manager_certs which can be used to manage the router default certificate via the configuration hierarchy.

Parameter secrets is intended for cases where a wildcard certificate has been purchased from a certificate authority.

Parameter cert_manager_certs allows users to configure a Certificate resource to request a wildcard certificate from a cert-manager issuer present on the cluster.

Fixes #16

Checklist

• [x] Keep pull requests small so they can be easily reviewed.
• [x] Update the documentation.
• [x] Categorize the PR by setting a good title and adding one of the labels: bug, enhancement, documentation, change, breaking, dependency as they show up in the changelog
• [x] Link this PR to related issues.
• [x] Rebase after #23 is merged
• [x] Use new cert-manager component lib version once https://github.com/projectsyn/component-cert-manager/pull/38 is merged.