[Internal] Refactor exporter: split huge files into smaller ones (#3870)

## Changes
<!-- Summary of your changes that are easy to understand -->

This PR splits `context.go` and `util.go` into smaller files, filled
with related functions, like, utils for workspace objects, utils for
SCIM (users/sps/groups), ...

## Tests
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How is this tested? Please see the checklist below and also describe any
other relevant tests
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- [x] `make test` run locally
- [ ] relevant change in `docs/` folder
- [ ] covered with integration tests in `internal/acceptance`
- [ ] relevant acceptance tests are passing
- [ ] using Go SDK