Auto-configured PrometheusPushGatewayManager cannot be configured to use HTTPS to connect to the gateway #16073
Description
The String-based PushGateway constructor that we use hardcodes an http scheme to the URL. We should switch to the URL-based constructor instead to allow users to specify an https URL via management.metrics.export.prometheus.pushgateway.base-url. We'll have to take care to do so in a backwards-compatible manner, probably by preserving the existing assumption that the scheme should be http if not specified.