Create LHCb specific version of MergingMultiTransformerFilter.

See merge request !3274

Release notes and dependencies for LHCb v53r3

See merge request !3276

RefBot going live!

See merge request !3272

Migrate to LHCb::Algorithm

See merge request !3267

Spruce reports to RawBanks, further cleanup of HltDAQ

See merge request !3260

Move Packing related algorithms to Event/EventPacker

See merge request !3269

add support for TH3 reading from conditions DB

See merge request !3208

- and thus, impliclicitly, to Gaudi::Algorithm
- also, migrate away from UTAlgBase:
   - specify DeUTDetector as dependency
   - use ToolHandle for readout tool
- prefer standalone functions in anonymous namespaces over member functions

LHCbAlgs: add missing MultiTransformerFilter in LHCb::Algorithms namespace

See merge request !3266

- remove support for run1-style 'joined' Hlt1/Hlt2 RawBank SourceID
  concretely: there must now be a one-to-one correspondence between the
  sourceID, and the list of decisions that need to be decoded.
- remove unused HltTrackReports{Writer,Decoder}
- factor out SourceID enum so a single definition can be shared
- add support for `Property<SourceID>` and use that instead of
  `Property<int>` + updatehandler or checks in initialize
- given the above, decoder components no longer have
  include their corresponding writer header files
- amalgamate component header files into the corresponding source files
- migrate HltDiffHltDecReports to LHCb::Algorithm::Consumer
- make HltLumiWriter thread-safe
- prefer MsgCounter over Error(...) and Warning(...)
- prefer span over bare pointer
- start putting code in the LHCb::Hlt::DAQ namespace instead of
  adding `using namespace LHCb`

Release notes and dependencies for LHCb v53r2

See merge request !3265