Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
CDC metrics, apart from tracking "total" metrics for all performed CDC
operations, also track metrics for "failed" operations. Because the
result of the CDC operation depends on whether all CDC mutations were
written successfully by storage_proxy, checking for failure and
incrementing appropriate counters is deferred after all write response
handlers finish.
The `cdc::operation_result_tracker` object was created for that purpose.
It contains all the details needed to accurately update the metrics
based on what actually happened in the `augment_mutation_call` function,
and holds a flag which tells if any of write response handlers failed.
This object is supposed to be referenced by write response handlers for
CDC mutations created after the same `augment_mutation_call`. After all
write response handlers are destroyed, the destructor of
`operation_result_tracker` will update appropriate metrics.
Actual creating and attaching this object to write response handlers
will be done in subsequent commits.
This patch defines a CDC metrics object and registers all of its
counters.
storage_proxy is chosen as the owner of the metrics object. Because in
subsequent commits it will become possible for CDC metrics to be updated
after a write operation ends, and because the cdc_service has shorter
lifetime than storage_proxy, we could risk a use-after-free if we placed
this object inside cdc_service.
