Add metric for BootstrappedAndDurable

[justinjc]

What this PR does / why we need it:

BootstrappedAndDurable is what is reported as "bootstrapped" by /health endpoint. Adding this metric gives us visibility in this database status without hitting the endpoint for that information.

Special notes for your reviewer: N/A

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

[codecov]

Codecov Report

Merging #2210 into master will decrease coverage by 5.5%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #2210     +/-   ##
========================================
- Coverage    72.2%   66.7%   -5.6%     
========================================
  Files        1022    1017      -5     
  Lines       89178   88488    -690     
========================================
- Hits        64440   59064   -5376     
- Misses      20447   25449   +5002     
+ Partials     4291    3975    -316

Flag	Coverage Δ
#aggregator	82% <ø> (+0.7%)	⬆️
#cluster	85.3% <ø> (-0.1%)	⬇️
#collector	82.8% <ø> (ø)	⬆️
#dbnode	79% <100%> (-0.1%)	⬇️
#m3em	73.4% <ø> (-1%)	⬇️
#m3ninx	69.1% <ø> (-3.3%)	⬇️
#m3nsch	17.9% <ø> (-33.2%)	⬇️
#metrics	17.6% <ø> (ø)	⬆️
#msg	74.9% <ø> (ø)	⬆️
#query	44.9% <ø> (-23.8%)	⬇️
#x	76.8% <ø> (-6.5%)	⬇️

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[robskillington]

LGTM