[dbnode] Add tracing for bootstrap process

[robskillington]

What this PR does / why we need it:

Adds tracing for DB node bootstrapping.

Special notes for your reviewer:

Does this PR introduce a user-facing and/or backwards incompatible change?:

NONE

Does this PR require updating code package or user-facing documentation?:

NONE

[arnikola]

Looks like may need to mockgen and maybe update a couple of tests unfortunately, LGTM otherwise

[codecov]

Codecov Report

Merging #2216 into master will decrease coverage by <.1%.
The diff coverage is 68.3%.

@@           Coverage Diff            @@
##           master   #2216     +/-   ##
========================================
- Coverage    72.4%   72.4%   -0.1%     
========================================
  Files        1022    1022             
  Lines       88865   88925     +60     
========================================
+ Hits        64386   64387      +1     
- Misses      20162   20206     +44     
- Partials     4317    4332     +15

Flag	Coverage Δ
#aggregator	82% <ø> (-0.1%)	⬇️
#cluster	85.3% <ø> (ø)	⬆️
#collector	82.8% <ø> (ø)	⬆️
#dbnode	79% <68.3%> (-0.2%)	⬇️
#m3em	74.4% <ø> (ø)	⬆️
#m3ninx	74.4% <ø> (ø)	⬆️
#m3nsch	51.1% <ø> (ø)	⬆️
#metrics	17.5% <ø> (ø)	⬆️
#msg	74.8% <ø> (-0.2%)	⬇️
#query	68.9% <ø> (ø)	⬆️
#x	83.2% <ø> (ø)	⬆️

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[robskillington]

Going to take @arnikola 's LGTM as a stamp.