[receiver/ntp] Enable re-aggregation feature

[dmitryax]

Part of #45396.

Enable the re-aggregation feature for the ntp receiver by:

1. Setting reaggregation_enabled: true in metadata.yaml
2. Ensuring all attributes are properly defined with appropriate levels:
   • required: cannot be reaggregated
   • recommended: enabled by default but can be disabled by users
   • opt_in: disabled by default but can be enabled by users
3. Validate the feature after the feature gate is enabled: all existing tests pass, manual check

[github-actions]

Pinging code owners:

• receiver/ntp: @atoulme @paulojmdias

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[Retr0-XD]

Hi @dmitryax! I would like to work on this issue. I have already implemented the changes:

• Added reaggregation_enabled: true to /receiver/ntpreceiver/metadata.yaml
• Updated changelog with enhancement entry
• Follows the established pattern from other receivers in the re-aggregation initiative

I will submit a PR shortly. Thank you!

[vyagh]

Hii, can I pick up this Issue?