vacuum tables on our own schedule

[owocki]

as you guys know, i have OCD about site speed. so today when the postgres auto vacuum er locked up the site, i had a conniption.

i wrote this quick script to turn off the auto vacuumer https://bits.owocki.com/bLum0Ene

and then i wrote this PR so we could vacuuum the site on our own schedule.. when load is lowest (sundays)

sample output:

root@f48599102c8a:/code/app# ./manage.py vacuum
dashboard_profilestathistory took 0.66s
quests_questfeedback took 0.05s
economy_conversionrate took 0.18s
feeswapper_currencyconversion took 0.07s
dashboard_blockedurlfilter took 0.02s
townsquare_like took 0.02s
faucet_faucetrequest took 0.03s
grants_update took 0.02s
marketing_accountdeletionrequest took 0.02s
dashboard_bounty took 1.97s
economy_token took 0.03s
auth_group took 0.02s
dashboard_coupon took 0.02s
townsquare_matchranking took 0.03s
avatar_socialavatar took 0.02s
tdi_accesscodes took 0.02s
django_session took 0.09s
gas_gasadvisory took 0.02s
marketing_alumni took 0.02s
townsquare_announcement took 0.02s

proof of sundays being the slow time for us:

[codecov]

Codecov Report

Merging #6138 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #6138      +/-   ##
=========================================
- Coverage   28.63%   28.6%   -0.03%     
=========================================
  Files         275     276       +1     
  Lines       24760   24779      +19     
  Branches     3619    3620       +1     
=========================================
  Hits         7089    7089              
- Misses      17394   17413      +19     
  Partials      277     277

Impacted Files	Coverage Δ
app/perftools/management/commands/vacuum.py	0% <0%> (ø)

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