code: Switch to seastar API level 7

In that level no io_priority_class-es exist. Instead, all the IO happens
in the context of current sched-group. File API no longer accepts prio
class argument (and makes io_intent arg mandatory to impls).

So the change consists of
- removing all usage of io_priority_class
- patching file_impl's inheritants to updated API
- priority manager goes away altogether
- IO bandwidth update is performed on respective sched group
- tune-up scylla-gdb.py io_queues command

The first change is huge and was made semi-autimatically by:
- grep io_priority_class | default_priority_class
- remove all calls, found methods' args and class' fields

Patching file_impl-s is smaller, but also mechanical:
- replace io_priority_class& argument with io_intent* one
- pass intent to lower file (if applicatble)

Dropping the priority manager is:
- git-rm .cc and .hh
- sed out all the #include-s
- fix configure.py and cmakefile

The scylla-gdb.py update is a bit hairry -- it needs to use task queues
list for IO classes names and shares, but to detect it should it checks
for the "commitlog" group is present.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

Closes #13963

db/view/build_progress_virtual_reader.hh

@@ -54,7 +54,6 @@ class build_progress_virtual_reader {
                 replica::column_family& scylla_views_build_progress,
                 const dht::partition_range& range,
                 const query::partition_slice& slice,
-                const io_priority_class& pc,
                 tracing::trace_state_ptr trace_state,
                 streamed_mutation::forwarding fwd,
                 mutation_reader::forwarding fwd_mr)
@@ -70,7 +69,6 @@ class build_progress_virtual_reader {
                         std::move(permit),
                         range,
                         slice,
-                        pc,
                         std::move(trace_state),
                         fwd,
                         fwd_mr))
@@ -192,7 +190,6 @@ public:
             reader_permit permit,
             const dht::partition_range& range,
             const query::partition_slice& slice,
-            const io_priority_class& pc,
             tracing::trace_state_ptr trace_state,
             streamed_mutation::forwarding fwd,
             mutation_reader::forwarding fwd_mr) {
@@ -202,7 +199,6 @@ public:
                 _db.find_column_family(s->ks_name(), system_keyspace::v3::SCYLLA_VIEWS_BUILDS_IN_PROGRESS),
                 range,
                 slice,
-                pc,
                 std::move(trace_state),
                 fwd,
                 fwd_mr));

db/view/view.cc

@@ -1898,7 +1898,6 @@ future<> view_builder::initialize_reader_at_current_token(build_step& step) {
             _permit,
             step.prange,
             step.pslice,
-            default_priority_class(),
             nullptr,
             streamed_mutation::forwarding::no,
             mutation_reader::forwarding::no);

db/view/view_update_generator.cc

@@ -10,7 +10,6 @@
 #include <boost/range/adaptor/map.hpp>
 #include "replica/database.hh"
 #include "view_update_generator.hh"
-#include "service/priority_manager.hh"
 #include "utils/error_injection.hh"
 #include "db/view/view_updating_consumer.hh"
 #include "sstables/sstables.hh"
@@ -147,11 +146,10 @@ future<> view_update_generator::start() {
                                 reader_permit permit,
                                 const dht::partition_range& pr,
                                 const query::partition_slice& ps,
-                                const io_priority_class& pc,
                                 tracing::trace_state_ptr ts,
                                 streamed_mutation::forwarding fwd_ms,
                                 mutation_reader::forwarding fwd_mr) {
-                        return ssts->make_range_sstable_reader(s, std::move(permit), pr, ps, pc, std::move(ts), fwd_ms, fwd_mr, *_progress_tracker);
+                        return ssts->make_range_sstable_reader(s, std::move(permit), pr, ps, std::move(ts), fwd_ms, fwd_mr, *_progress_tracker);
                     });
                     auto [staging_sstable_reader, staging_sstable_reader_handle] = make_manually_paused_evictable_reader_v2(
                             std::move(ms),
@@ -159,7 +157,6 @@ future<> view_update_generator::start() {
                             permit,
                             query::full_partition_range,
                             s->full_slice(),
-                            service::get_local_streaming_priority(),
                             nullptr,
                             ::mutation_reader::forwarding::no);
                     auto close_sr = deferred_close(staging_sstable_reader);