[SKA] relocate oblt functional tests

[dmlemeshko]

Summary

Part of https://github.com/elastic/kibana-team/issues/1503

This PR is mostly about moving oblt functional tests from x-pack/test

x-pack/test/functional/apps/
     | - apm/
     | - dataset_quality/
     | - infra/
     | - slo/
x-pack/test/observability_functional
x-pack/test/observability_api_integration

After:

x-pack/solutions/observability/test/functional/apps
     | - apm/
     | - dataset_quality/
     | - infra/
     | - slo/
x-pack/solutions/observability/test/observability_functional
x-pack/solutions/observability/test/observability_api_integration

[elasticmachine]

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[elasticmachine]

💔 Build Failed

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• Commit: ec4b714

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• 💔 Build #316344 failed bdaa0f3
• 💔 Build #316214 failed 167aab5
• 💔 Build #316196 failed 24b6499

[dmlemeshko]

closed in favour of #227754