[Asset Inventory] Add event.category and event.module to all events

[kubasobon]

Summary of your changes

• Adds event.category to all Events published by Asset Inventory. The values are compliant with the ECS.
• Adds event.module: asset discovery to all Events

Related Issues

Closes #3890

[mergify]

This pull request does not have a backport label. Could you fix it @kubasobon? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[JordanSh]

LGTM 👑

[kubasobon]

@uri-weisman Added event.module: asset discovery as well, just like we talked.

[uri-weisman]

99% sure we should use an underscore for ECS field value, so - asset_discovery
In addition, we need to check the dataset naming because it should start with the module name.

"It's recommended but not required to start the dataset name with the module name, followed by a dot, then the dataset name. "

[kubasobon]

Hmm, we don't publish dataset names. I think provider makes sense? As in asset_discovery.aws, asset_discovery.gcp, etc. WDYT?

[uri-weisman]

💯
Just @caitlinbetz validating with you before pushing this.
We plan to add event.module: asset_discovery and event.dataset: asset_discovery.<CLOUD_PROVIDER> to the asset discovery integration.