Metrics based alert rules

[Abuelodelanada]

Issue

This PR adds Loki metric based alert rules for its relation with Prometheus.

Testing Instructions

• Deploy Loki
• Deploy Prometheus
• Relate both charms
• Check Loki Alert rules are present in Prometheus

Integration test should be added in COS-Lite

[github-actions]

Libraries are not up to date with their remote counterparts. If this was
not intentional, run charmcraft fetch-libs and commit the updated libs
to your PR branch.

stdout

Library charms.alertmanager_k8s.v0.alertmanager_dispatch was already up to date in version 0.4.                                                                
Library charms.grafana_k8s.v0.grafana_source was already up to date in version 0.10.                                                                           
Library charms.loki_k8s.v0.loki_push_api has local changes, cannot be updated. 
Library charms.observability_libs.v0.juju_topology was already up to date in version 0.2.                                                                      
Library charms.observability_libs.v0.kubernetes_service_patch was already up to date in version 0.6.                                                           
Library charms.prometheus_k8s.v0.prometheus_scrape was already up to date in version 0.20.                                                                     
Library charms.traefik_k8s.v0.ingress_per_unit was already up to date in version 0.10.                                                                         

stderr

[github-actions]

Libraries are not up to date with their remote counterparts. If this was
not intentional, run charmcraft fetch-libs and commit the updated libs
to your PR branch.

stdout

Library charms.alertmanager_k8s.v0.alertmanager_dispatch was already up to date in version 0.4.                                                                
Library charms.grafana_k8s.v0.grafana_source was already up to date in version 0.10.                                                                           
Library charms.loki_k8s.v0.loki_push_api has local changes, cannot be updated. 
Library charms.observability_libs.v0.juju_topology was already up to date in version 0.2.                                                                      
Library charms.observability_libs.v0.kubernetes_service_patch was already up to date in version 0.6.                                                           
Library charms.prometheus_k8s.v0.prometheus_scrape was already up to date in version 0.20.                                                                     
Library charms.traefik_k8s.v0.ingress_per_unit was already up to date in version 0.10.                                                                         

stderr

[github-actions]

Libraries are not up to date with their remote counterparts. If this was
not intentional, run charmcraft fetch-libs and commit the updated libs
to your PR branch.

stdout

Library charms.alertmanager_k8s.v0.alertmanager_dispatch was already up to date in version 0.4.                                                                
Library charms.grafana_k8s.v0.grafana_source was already up to date in version 0.10.                                                                           
Library charms.loki_k8s.v0.loki_push_api has local changes, cannot be updated. 
Library charms.observability_libs.v0.juju_topology was already up to date in version 0.2.                                                                      
Library charms.observability_libs.v0.kubernetes_service_patch was already up to date in version 0.6.                                                           
Library charms.prometheus_k8s.v0.prometheus_scrape was already up to date in version 0.20.                                                                     
Library charms.traefik_k8s.v0.ingress_per_unit was already up to date in version 0.10.                                                                         

stderr