Add bio field for user

[techknowlogick]

Fix #4339

user with simple bio:

user with no bio:

user with xss attempt that was escaped:

[codecov-io]

Codecov Report

Merging #6113 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #6113      +/-   ##
==========================================
- Coverage   38.88%   38.87%   -0.02%     
==========================================
  Files         364      365       +1     
  Lines       51215    51341     +126     
==========================================
+ Hits        19916    19959      +43     
- Misses      28432    28509      +77     
- Partials     2867     2873       +6

Impacted Files	Coverage Δ
models/user.go	49.76% <ø> (ø)	⬆️
modules/auth/user_form.go	42.85% <ø> (ø)	⬆️
routers/user/setting/profile.go	40.81% <100%> (+0.4%)	⬆️
models/webhook.go	63.18% <0%> (-5.54%)	⬇️
modules/context/api.go	50.61% <0%> (-0.21%)	⬇️
models/repo.go	47.36% <0%> (-0.09%)	⬇️
routers/repo/webhook.go	1.73% <0%> (-0.05%)	⬇️
routers/admin/hooks.go	0% <0%> (ø)
routers/routes/routes.go	83.44% <0%> (+0.36%)	⬆️
routers/repo/view.go	42.07% <0%> (+0.99%)	⬆️
... and 1 more

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[zeripath]

I think LDAP also has a user description attribute - although I'm not sure how many installs use it.