[DPE-5330][DPE-5334] Update to 2.15.0

[phvalguima]

Updates the charm to use opensearch 2.15, built from source.

This opensearch version also contains patches backported for ml-commons and security:

• https://github.com/opensearch-project/ml-commons/commit/0a6a2b06619945615e800c61e2979822faf29904
• https://github.com/opensearch-project/security/commit/64b842ece6e91064a954c4c2dd7ea109da52af2f