GraphQL: Allow a keyset_connection to support multiple ordering attributes

What does this MR do?

Our current Gitlab::Graphql::Connections::KeysetConnection only supports ordering on one attribute. To properly support ordering on multiple attributes and ensuring that cursor based ordering will return proper results, we need to be able to order on multiple attributes, such as Issue.order(:udpated_at).order(:id)

We can now store the necessary attributes in the cursor (such as a node's updated_at and id value), in order to properly get back nodes in relation to the cursor. We do this by storing the attributes in a json structure and then encoding that into the cursor.

Related issue: #29713 (closed)

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Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
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Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

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