Update otelcol test package

[jsoriano]

Update otelcol test package following current recommendations:

• Dataset in OTel packages should default to the related community receivers (see System tests for OTel policies must check that the default policy template name matches with the expected receiver #2974).
• subobjects: false at the root level conflicts with built-in templates (after [Fleet] Install only OTel component template mappings for otelcol inputs kibana#237165).
• No fields are needed (requires Input packages don't require to define fields package-spec#994).

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 8dfe41b

History

• 💔 Build #6296 failed 3942c3e
• 💔 Build #6295 failed d4b0aed
• 💔 Build #6273 failed 328ea22

cc @jsoriano