Skip updates for webhooks upserts

[Simply007]

Motivation

Check modified date of the updated item vs modified date of an item that is already in the graphql model.

Proposed solution

Do not make an update if the latest version is already pushed.

Additional context

When there are a lot of changes in one node, some of the updates could load the latest version sooner so that it is not necessary to reupdate the same content again.
It should help the processing and save some RTE updates.

[Simply007]

In the webhook message, there is just the information, when the webhook was triggered not the last modified date at that time + since the webhooks receiving does not preserve order, this date should not be used nor overriding last modified date.

It is necessary to load Kontent Item for every upsert webhook and then decide whether to perform an update by comparing system.last_modified of the already created Node vs. newly loaded data.