Disable memory circuit breaker for integ tests

[martin-gaievski]

Description

Adapt fix in memory circuit breaker of ml-commons (https://github.com/opensearch-project/ml-commons/pull/2469) to integ tests. Doing following:

• lower heap memory allocation for test cluster from 4 to 2Gb. It has been increased to 4Gb under https://github.com/opensearch-project/neural-search/pull/500 to lower the chance of test failure
• disable memory CB of ml-commons for all integ tests. that will ensure every test executed in cluster with disabled memory CB

Issues Resolved

https://github.com/opensearch-project/neural-search/issues/689

Check List

• [x] All tests pass
• [X] Commits are signed as per the DCO using --signoff

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