[Search Session] Use server-side authc.getCurrentUser from core.security

[tsullivan]

Part of #186574

Background: This PR serves as an example of a plugin migrating away from depending on the Security plugin, which is a high priority effort for the last release before 9.0. The Search Session service uses the authc.getCurrentUser method as a means to create a scoped client with methods that filters saved search sessions to the current user.

Checklist

Delete any items that are not applicable to this PR.

• Unit or functional tests were updated or added to match the most common scenarios

[tsullivan]

/ci

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 026c26f

Failed CI Steps

• Jest Integration Tests #5

Metrics [docs]

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
data	54	55	+1

References to deprecated APIs

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data	29	28	-1

Total ESLint disabled count

id	before	after	diff
data	56	57	+1

History

• 💛 Build #217750 was flaky dad263f

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