chore(slo): use CCS Remote index name util function

[kdelemme]

Resolves #194141

Summary

This PR uses the new util function for parsing CCS remote index name instead of relying on .includes(":")

[elasticmachine]

Pinging @elastic/obs-ux-management-team (Team:obs-ux-management)

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 1478f3b

Failed CI Steps

• FTR Configs #6

Test Failures

• [job] [logs] FTR Configs #6 / Spaces app space solution tour solution tour does not show the solution tour after deleting spaces and leave only the default

Metrics [docs]

✅ unchanged

cc @kdelemme

[kibanamachine]

Starting backport for target branches: 8.x

https://github.com/elastic/kibana/actions/runs/12588151134

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[kdelemme]

💚 All backports created successfully

Status	Branch	Result
✅	8.x

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Looks like this PR has a backport PR but it still hasn't been merged. Please merge it ASAP to keep the branches relatively in sync.