Read operator privs enabled from Env settings

[tvernum]

Security.settings incorrectly caches the node startup settings which does not take into account setting changes that may take place after the node has started (e.g. "addtionalSettings()" from plugins).

This commit fixes the behaviour for the OperatorPrivileges enabled setting, until the bug can be fixed more generally

[elasticsearchmachine]

Hi @tvernum, I've created a changelog YAML for you.

[elasticsearchmachine]

Pinging @elastic/es-security (Team:Security)

[tvernum]

I'd love to fix the bug more generally - this TODO has been around for far too long, but it required making settings not final, which is a can of worms that I can't get through today.

elasticsearch/x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/Security.java

Lines 560 to 561 in c9c2f76

	// TODO This is wrong. Settings can change after this. We should use the settings from createComponents
	this.settings = settings;

[ywangd]

LGTM

FWIW, I had to do something similar for the recent work of supporting overridden builtin roles.

[jakelandis]

Thanks for fixing !