[Logstash Plugin] Migrate authc.getCurrentUser usage to coreContext.security

[tsullivan]

Part of https://github.com/elastic/kibana/issues/186574

Summary

This PR migrates the Logstash Plugin's route handler for saving a pipeline, which consumes authc.getCurrentUser, to use coreContext.security.

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.

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

[tsullivan]

/ci

[kibana-ci]

:yellow_heart: Build succeeded, but was flaky

• Buildkite Build
• Commit: 398a800bbfe5806cd1ff3cdedacb96d3dcf32501

Failed CI Steps

Metrics [docs]

Unknown metric groups

References to deprecated APIs

id	before	after	diff
logstash	2	1	-1

History

• :yellow_heart: Build #218566 was flaky eeb396bef7e21f32e082a6c84869aad52c9301a6
• :broken_heart: Build #218563 failed c7bfb4d80c4dfa09db07b7bbf7533b7f84f1260c

To update your PR or re-run it, just comment with: @elasticmachine merge upstream

[elasticmachine]

:yellow_heart: Build succeeded, but was flaky

• Buildkite Build
• Commit: 0c71f4ec6d3b74a6cc7c966ea9f31bb3477778cd

Failed CI Steps

• Jest Tests #4
• FTR Configs #73

Metrics [docs]

Unknown metric groups

References to deprecated APIs

id	before	after	diff
logstash	2	1	-1

History

• :broken_heart: Build #219223 failed cf126a9228f90a028ee5ebb28d9968a7db810aed