feat: add super properties

[daibhin]

Problem

Customers of error tracking want to know what repository a particular exception came from by filtering in the UI. Rather than adding some specific property (e.g. exception_source_identifier) that would then need to be added to the JS SDK and any other language we support in future, I thought it would be easier to reuse the super properties concept found in our other SDKs

I'm not tied to this approach but "PRs > Slack" and all that... Open to feedback here.

Changes

• Went with a very basic implementation that allows you to set super_properties when initialising the client
  • Could have gone with the register method seen elsewhere but didn't want to mislead customers into thinking that properties were somehow stored elsewhere (like they are in local storage). Better to make sure that they're always included when the client is initialised

[neilkakkar]

One blocking comment, otherwise LGTM! Pragmatic approach to adding it on sdk init, I like it

[neilkakkar]

(also remember to bump version and changelog before merging)

[neilkakkar]

noice