feat: Replace the requirer's rule interface with a rules object

[MichaelThamm]

Context

Blocked by these PRs:

• refactor: Improve testing and docs #375
• feat: Type-agnostic Rules instance cos-lib#187

Blocking this PR:

• feat: New usage of otlp lib with the Rules interface opentelemetry-collector-k8s-operator#202

Why is this needed?

This PR allows users of the lib to build a rules object (built around the cosl.rules.Rules class) and pass that to the OtlpRequirer for publishing to the databag. The library adds its own rules to this object e.g., generic alert rules prior to publishing to the relation databag. The RuleStore is the API used to build the rules object which has a similar API to the cosl.rules.Rules class which uses the add and add_path methods to store rules.

API

Old

class OtlpRequirerCharm(CharmBase):
    def __init__(self, framework: ops.Framework):
        super().__init__(framework)
        self.framework.observe(self.on.update_status, self._on_update_status)

    def _on_update_status(self, event: ops.EventBase) -> None:
        OtlpRequirer(
            self,
            protocols=['http', 'grpc'],
            telemetries=['metrics', 'logs'],
            loki_rules_path=self.charm_root.joinpath(*LOKI_RULES_DEST_PATH.split('/')),
            prometheus_rules_path=self.charm_root.joinpath(*METRICS_RULES_DEST_PATH.split('/')),
        ).publish()

New

class OtlpRequirerCharm(CharmBase):
    def __init__(self, framework: ops.Framework):
        super().__init__(framework)
        self.framework.observe(self.on.update_status, self._publish_rules)

    def _publish_rules(self, _: ops.EventBase) -> None:
        rules = (
            RuleStore(JujuTopology.from_charm(self))
            .add_logql(SINGLE_LOGQL_ALERT, group_name='test_logql_alert')
            .add_logql(SINGLE_LOGQL_RECORD, group_name='test_logql_record')
            .add_promql(SINGLE_PROMQL_ALERT, group_name='test_promql_alert')
            .add_promql(SINGLE_PROMQL_RECORD, group_name='test_promql_record')
            .add_logql(OFFICIAL_LOGQL_RULES)
            .add_promql(OFFICIAL_PROMQL_RULES)
        )
        OtlpRequirer(
            self, protocols=ALL_PROTOCOLS, telemetries=ALL_TELEMETRIES, rules=rules
        ).publish()