Update OWNER files to include all team members

[knottnt]

Issue #, if available:

Description of changes:

• Remove service_team alias
• Move old team members to emeritus comment
• Add jlbutler, michaelhtm, rushmash91, and knottnt to core-team

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[ack-prow]

@knottnt: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
firehose-verify-attribution	79cc7b2	link	false	/test firehose-verify-attribution

Full PR test history. Your PR dashboard.

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[a-hilaly]

/lgtm

[ack-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: a-hilaly, knottnt

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• OWNERS [a-hilaly]

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