Update GET _cluster/health response to distinguish RED cluster from n…

[getsaurabh02]

…o-master (#34897)

Added boolean "discovered_master": true in the GET _cluster/health response to expose the presence of master.

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[elasticmachine]

Pinging @elastic/es-distributed

[getsaurabh02]

Hey,

Awaiting review. Thanks.

[getsaurabh02]

Hi,

Awaiting Response.

[DaveCTurner]

Sorry for the delay @getsaurabh02, we looked at the original issue again and worked out that we can obtain the behaviour we want already, so there is no need to make this change.