[Status API] Add build_hash for non-distributable deployments

[sorenlouv]

Currently build_hash is XXX...X for non-distributable deployments of Kibana:

Would it be possible to fall back to the actual git version by changing this:

kibana/src/core/server/config/env.ts

Line 133 in 3af2f60

buildSha: isKibanaDistributable ? pkg.build.sha : 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX',

To something like:

const currentCommitHash = () => exec('git rev-parse HEAD')
// ...
return {
  buildSha: isKibanaDistributable ? pkg.build.sha : currentCommitHash(), 
}

For development purposes we have dev clusters deployed directly from source, and having the same information available as with distributables would be very helpful.

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[pgayvallet]

Even if only in development mode, I've got mixed feeling about invoking git directly from Env. It's also leading to hard to mock value in test environment. OTOH I don't really see any risk if properly wrapped in a try/catch block with fallback to the actual XXX...

Anyone else got a stronger opinion?