The main purpose is to replace context.TODO with a context provided by the
caller. A secondary purpose is to enable contextual logging.

Modifying the existing interfaces and APIs would have a big impact on the
ecosystem. This is a no-go. Instead, the following approach was taken:

- All interfaces get duplicated in a *WithContext variant where the methods
  also have a *WithContext suffix and the ctx parameter. All methods are
  treated this way except for obvious local get methods (like RESTClient)
  because it cannot be ruled out entirely that some implementation may
  need a context.

- Implementations of these interfaces implement both method variants
  which is possible because the method names are different.
  The old methods are implemented as thin wrappers around the updated
  code which is now the body of the new methods or shared helpers.
  In some cases there is additional overhead (type checks, potentially
  additional allocations) when using the old methods.

- To*WithContext helpers bridge from the old to the new interfaces. They
  try a type cast first. Because the in-tree implementations implement
  both, they can be used directly. For other implementations wrappers
  are used.

- All old APIs and interfaces are marked as deprecated. There is no
  intent to ever remove them, but consumers should be made aware
  that there are now better alternatives. Implementations also
  get marked this way even if nothing ever calls them directly
  because it shows which code, at least theoretically, could get
  removed.

- Existing unit tests do not get updated to the new APIs. This gives
  us unit test coverage of the old and new API because the old
  APIs call the new ones.

- In-tree consumers will be updated in follow-up PRs. This is likely
  to be a longer process. Because of the deprecation comment,
  `hack/golangci-lint.sh -n` can be used to find code which needs
  to be updated.

When debugging, it helps to keep output from different connections
separate. This can be done with contextual logging and using different loggers
for each connection.

Cancellation is handled separately for requests. Therefore the new APIs only
add support for passing a logger instance.

The API for the package already had a context, so all that was missing was to
extract and use the logger from that.

The remaining non-structured, non-contextual log calls hopefully never get
reached, so it's not worth converting them.

This changes the log output of kubectl, which affects some test cases which
check for GET results in that log output.