impr/clients: Handle TLS config and MTLS for logcli and promtail (gra…

…fana#540)

* impr/clients: Handle TLS config and MTLS for logcli and promtail

* fix/tls: Please gofmt...

* impr/clients: use prometheus HTTPClientConfig for logcli and promtail

* fix/promtail: Set proper Client config name

* impr/promtail: Use prometheus HTTPClientConfig configuration

* adapt with master

* address review

* fix conflicts

* address requested changes

* remove file