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
This one works similar to `serializer<optional<T>>` and will be
later needed for serializing `raft::append_request`, which has
a field containing `lw_shared_ptr`.
Users to be warned, though: this code assumes that the pointer
is never null. This is done to mirror the serialize implementation
for `lw_shared_ptr:s` in the messaging_service.cc, which is
subject to being deleted in favor of the impl in the
`serializer_impl.hh`.
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
