[Bug] @elastic/elasticsearch should be a peerDependency

[Bamieh]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

latest

Plugin version

latest

Description

The dependancy @elastic/elasticsearch should be a peerDependency inside the package.json file instead of a regular dependency. This allows the host package to specify the elasticsearch version it will be using.

Currently all ts types break because of incompaible client versions if we are using other versions than the latest one enforced by this package, while this package does not care about that and we can specify the client externally anyways.

Expected Behavior

Host pacakge to install @elastic/elasticsearch@ and this package to be able to specify the elasticsearch version they are using.

[mcollina]

I'm not sure that would work well - what if the @elastic/elasticsearch client changes API?

Anyhow, I'd be good for this change if CI would test all the available majors that would be supported. Would you like to send a PR?