Add REST endpoint to retrieve current user information

[vinokurig]

What does this PR do?

Add REST endpoint to retrieve current user information.

Screenshot/screencast of this PR

What issues does this PR fix or reference?

https://redhat.atlassian.net/browse/CRW-10682

How to test this PR?

1. Apply the che-server image: quay.io/eclipse/che-server-pr:1018
2. Execute the API request: <che-endpoint>/api/user.
3. See: User object received:

PR Checklist

As the author of this Pull Request I made sure that:

• The Eclipse Contributor Agreement is valid
• Code produced is complete
• Code builds without errors
• Tests are covering the bugfix
• The repository devfile is up to date and works
• Sections What issues does this PR fix or reference and How to test this PR completed
• Relevant user documentation updated
• Relevant contributing documentation updated
• CI/CD changes implemented, documented and communicated

Release Notes

Reviewers

Reviewers, please comment how you tested the PR when approving it.

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: vinokurig

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[github-actions]

Docker image build succeeded: quay.io/eclipse/che-server:pr-1018

kubectl patch command

kubectl patch -n eclipse-che "checluster/eclipse-che" --type=json -p="[{"op": "replace", "path": "/spec/components/cheServer/deployment", "value": {containers: [{image: "quay.io/eclipse/che-server:pr-1018", name: che}]}}]"

[vinokurig]

/retest

[vinokurig]

/retest