Restrict files permissions

[frantz45]

With current permissions there are many warning logs complaining about "insecure file permissions" when you start the service.
Restrict acces only to the opensearch user and remove permissions for the group.
So instead of 750 for directory it should be 700.
Instead of 640 for files it should be 600.

[smortex]

Related: #34

See (and raise your voice in 😄) discussions with upstream:

• Defaut config permission too relaxed in deb and rpm packages opensearch-project/opensearch-build#3815
• [Meta] Improve Deb/Rpm OpenSearch packaging in 2.x Releases opensearch-project/opensearch-build#4087

[roock]

Version 2.13 has a changed default package permissions:
opensearch-project/opensearch-build#4043