Update data classification standard: use "Customer's Data" consistently

## Purpose

The Data Classification Standard defines data type and categories and provides the associated Data Classification of each for the purposes of determining the level of protection to be applied to GitLab and Customer data throughout its lifecycle.

The Data Classification Standard defines data type and categories and provides the associated Data Classification of each for the purposes of determining the level of protection to be applied to GitLab and Customer's Data throughout its lifecycle.

## Scope

Examples include:

- Customer Data (see definition above in the [Data Classification Definitions section](/handbook/security/policies_and_standards/data-classification-standard/#data-classification-definitions))

- Customer's Data (see definition above in the [Data Classification Definitions section](/handbook/security/policies_and_standards/data-classification-standard/#data-classification-definitions))

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##### REGULATED RED