[CT-2522] Redefine Metric node for the Manifest and update parsing

[QMalcolm]

There are two new node types being added to the manifest as part of the MetricFlow integration work: SemanticModel nodes and Metric nodes. This ticket addresses the Metric nodes. In dbt-semantic-interfaces we're adding a protocol of a Metric, which will have the shared standard definition of a Metric. In dbt-core we need to compose this protocol with base node classes to define dbt-core's representation of a Metric. Additionally there are some additional fields we should expose as defined in #7456

Blocked by:

• [CT-2496] [Spike] Determine best practices for composing nodes with python Protocols #7470
• Create protocol abstraction for Metrics dbt-semantic-interfaces#18

[emmyoop]

This should be done along with the issue to parse the new metric node so that we don't start breaking tests - #7501

[QMalcolm]

An update on context. dbt-core already has a concept of a Metric Node from dbt-metrics. Thus instead removing and re-adding metric nodes, what we're really doing is redefining metric nodes to match the spec defined in dbt-semantic-interfaces. Additionally, since metric nodes already exist we don't need to build parsing for them, but instead just update the parsing. Thus #7501 is being wrapped into the work of this issue.