GraphQL: Update customer endpoint docs for 2.3.1

[keharper]

Community engineering issue

Type of Doc:

• New topic
• Topic Update, Devdoc link:
• Other

Magento 2 GitHub Issue: Various. See the links within the graphql-ce PRs

Magento 2 GitHub PRs:

magento/graphql-ce#150
magento/graphql-ce#162
magento/graphql-ce#180
magento/graphql-ce#187
magento/graphql-ce#194
magento/graphql-ce#195
magento/graphql-ce#225
magento/graphql-ce#254

Magento 2 version:

• 2.1.X
• 2.2.X
• 2.3.1
• back port
• forward port

Notifications of Changes:

• Changes to Admin interface?
• New software requirements?
• New REST endpoints or updated GraphQL query syntax?
• New command line option?

Content

Several PRs that add mutations or query parameters for the customer endpoint have been checked in recently. This issue tracks the documentation effort from one place.

Note: PR-150 and 180 are labeled as 2.3.0, but they're not in the 2.3.0-release branch.