feat(slo): Show SLI preview chart for custom kql

[kdelemme]

Related to https://github.com/elastic/actionable-observability/issues/42

Summary

This PR introduces a SLI preview chart on the SLO form creation for Custom KQL indicator type.
The goal is to help the user building the right query for its SLO, without having to save and wait for the data to be rolled up.

Description	Screenshot
When the indicator is valid, we show the data if any
When indicator is invalid: we show no chart
When the data is loading

[apmmachine]

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• /oblt-deploy : Deploy a Kibana instance using the Observability test environments.
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[elasticmachine]

Pinging @elastic/actionable-observability (Team: Actionable Observability)

[simianhacker]

LGTM

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: a9a2eec

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
observability	431	434	+3

Public APIs missing comments

Total count of every public API that lacks a comment. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats comments for more detailed information.

id	before	after	diff
@kbn/slo-schema	111	115	+4

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
observability	1021.5KB	1024.0KB	+2.4KB

Unknown metric groups

API count

id	before	after	diff
@kbn/slo-schema	111	115	+4

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	13	15	+2
observability	38	39	+1
securitySolution	411	415	+4
total			+7

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	14	16	+2
observability	43	44	+1
securitySolution	494	498	+4
total			+7

History

• 💚 Build #135736 succeeded e263720c60f4f3d5acdd6c0061de44f522ad7c9f
• 💚 Build #135364 succeeded cdebff6c2d94b340c643e25dcf636223c93df80f
• 💔 Build #135345 failed 3b3669bc4dfea61f05af13be41a53f81b6cfb79f
• 💔 Build #135252 failed 4cee50e36631ff222e3ee80f182716fe7c69a32a

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@elasticmachine merge upstream

cc @kdelemme