Remove BaseDendrite

[S7evinK]

Removes BaseDendrite to, hopefully, make testing and composing of components easier in the future.

[codecov]

Codecov Report

Patch coverage: 80.22% and project coverage change: +0.16 🎉

Comparison is base (ec6879e) 63.24% compared to head (a09828b) 63.40%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3023      +/-   ##
==========================================
+ Coverage   63.24%   63.40%   +0.16%     
==========================================
  Files         497      497              
  Lines       53851    53745     -106     
==========================================
+ Hits        34058    34077      +19     
+ Misses      16100    16014      -86     
+ Partials     3693     3654      -39     

Flag	Coverage Δ
unittests	42.85% <80.22%> (-0.11%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/dendrite/main.go	75.00% <ø> (-5.00%)	⬇️
roomserver/internal/alias.go	53.19% <0.00%> (-2.84%)	⬇️
roomserver/internal/input/input.go	77.44% <0.00%> (+4.68%)	⬆️
setup/base/sanity_unix.go	27.27% <0.00%> (-4.55%)	⬇️
setup/jetstream/nats.go	52.22% <0.00%> (-1.32%)	⬇️
setup/base/base.go	52.66% <38.09%> (-4.43%)	⬇️
mediaapi/routing/routing.go	71.15% <50.00%> (-1.93%)	⬇️
setup/mscs/msc2836/msc2836.go	42.71% <75.00%> (ø)
clientapi/routing/routing.go	54.61% <77.77%> (-0.01%)	⬇️
federationapi/routing/routing.go	77.35% <80.00%> (-0.24%)	⬇️
... and 16 more

... and 47 files with indirect coverage changes

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[kegsay]

This is an improvement on the status quo because we now have each component only accepting what they actually need rather than BaseDendrite everywhere. The component constructors are still very complex at present, but we can make composable intermediate structs in another PR. LGTM