[Docs] Security: Event Audit Trail

#### Current State
The Security feature for [event audit trail ](https://cloud.layer5.io/events/audit)is not documented.

#### Desired State
Create a new page describing this feature.

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#### Contributor Guide and Resources
- 📚 [Instructions for contributing to documentation](https://github.com/layer5io/docs/blob/master/CONTRIBUTING.md)
- Layer5 documentation [site](https://docs.layer5.io) and [source](https://github.com/layer5io/docs/)
- 🎨 Wireframes and [designs for Layer5 site](https://www.figma.com/file/5ZwEkSJwUPitURD59YHMEN/Layer5-Designs) in Figma [(open invite)](https://www.figma.com/team_invite/redeem/qJy1c95qirjgWQODApilR9)
- 🙋🏾🙋🏼 Questions: [Layer5 Discussion Forum](https://discuss.layer5.io) and [Layer5 Community Slack](http://slack.layer5.io)