Create endpoint to get Gaffer version

[t92549]

Describe the new feature you'd like
An endpoint added to the rest api to get the api's Gaffer version

Why do you want this feature?
Swagger does give this information but with the upgrade to swagger version, how to get it is inconsistent. It is important to know what Gaffer version an api is running and therefore it would be better if this was provided by the api.

Additional context
This should probably be added to both the spring-rest and core-rest

[GCHQDev404]

Its unfortunate but upon inspection of the PR the ticket is not correct.
The version should be accessible and be supported in a Federated System with multiple stores/graphs.

The approach likely should be a Operation and Handler to get the version, which can then be delegated to individual graphs using a normal FederatedOperation

[tb06904]

Its unfortunate but upon inspection of the PR the ticket is not correct. The version should be accessible and be supported in a Federated System with multiple stores/graphs.

The approach likely should be a Operation and Handler to get the version, which can then be delegated to individual graphs using a normal FederatedOperation

Isn't that a separate feature? It seems like from the original ticket its just the API version of what you are interacting with that should be returned which if it was a federated system would still work and just be the version of the graph configured with a federated store.
What you are suggesting with a Federated Operation sounds like a separate feature that could co exist with this to get a list of sub graph versions?

[GCHQDeveloper314]

An operation to get the Gaffer version is a separate, but related feature. An operation could be federated to a remote graph, which might be running a different version of Gaffer to the version running the REST API a user is directly interacting with. This comment explains further, but for getting the store type.

A GetGafferVersion operation could be created under a separate ticket. It could take the work to create an endpoint and reuse this in an operation which the endpoint would then call. As has been done for the GetTraits endpoint and operation. But this wouldn't be the correct approach for certain stores, see below.

The endpoint will always return the version of Gaffer used by the REST instance. This is less useful than an operation which can be used to determine the version of Gaffer used by remote stores. However, if the endpoint is a Proxy Store, then any operations sent to it will always be processed by the remote store it's connected to. So using only an operation, it wouldn't be possible to get the Gaffer version used by a Proxy Store REST endpoint itself. The situation would be the same for a Federated Store endpoint which federated only to remote graphs.

I think that an operation would also be useful, and an endpoint would not be redundant, they would not have identical functionality.