This commit rewrites the `BucketReconciler` to new standards, while
implementing the newly introduced Condition types, and trying to
adhere better to Kubernetes API conventions.

More specifically it introduces:

- Implementation of more explicit Condition types to highlight
  abnormalities.
- Extensive usage of the `conditions` subpackage from `runtime`.
- Better and more conflict-resilient (status)patching of reconciled
  objects using the `patch` subpackage from runtime.
- Proper implementation of kstatus' `Reconciling` and `Stalled`
  conditions.
- Refactor of reconciler logic, including more efficient detection of
  changes to bucket objects by making use of the etag data available,
  and downloading of object files in parallel with a limited number of
  workers (4).
- Integration tests that solely rely on `testenv` and do not
  use Ginkgo.

There are a couple of TODOs marked in-code, these are suggestions for
the future and should be non-blocking.
In addition to the TODOs, more complex and/or edge-case test scenarios
may be added as well.

Signed-off-by: Hidde Beydals <hello@hidde.co>

This commit consolidates the `DownloadFailed` and `CheckoutFailed`
Condition types into a new more generic `FetchFailed` type to simplify
the API and observations by consumers.

Signed-off-by: Hidde Beydals <hello@hidde.co>

Add `BucketReconciler.reconcileArtifact` tests based on
`GitRepositoryReconciler.reconcileArtifact` test cases.

Signed-off-by: Sunny <darkowlzz@protonmail.com>

This wraps the errors which are returned instead of logging them, as
the returned error is logged at the end of the reconcile run.

Signed-off-by: Hidde Beydals <hello@hidde.co>