[cmd/mdatagen] Consolidate resource building

Use the recently introduce ResourceBuilder in MetricsBuilder instead of generating separate logic. This consolidation will make all the future improvements to the ResourceBuilder applicable for craping receivers and resource processors. This also opens the door for getting away from the sequential ResourceMetrics building using EmitForResource towards better structured map-based approach.

.chloggen/mdatagen-apply-resource-builder-on-metrics.yaml

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+# Use this changelog template to create an entry for release notes.
+# If your change doesn't affect end users, such as a test fix or a tooling change,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: cmd/mdatagen
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Simplify resource building in MetricsBuilder, suggest using ResourceBuilder instead.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [24443]