Prepare v0.12.0 release

[Aneurysm9]

No description provided.

[MrAlias]

LGTM with the minor link fix 👍

[codecov]

Codecov Report

Merging #1205 into master will decrease coverage by 0.3%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #1205     +/-   ##
========================================
- Coverage    76.8%   76.5%   -0.4%     
========================================
  Files         134     134             
  Lines        5735    5760     +25     
========================================
  Hits         4410    4410             
- Misses       1083    1108     +25     
  Partials      242     242             

Impacted Files	Coverage Δ
sdk/opentelemetry.go	100.0% <ø> (ø)
sdk/export/metric/exportkind_string.go	66.6% <0.0%> (-33.4%)	⬇️
label/type_string.go	7.1% <0.0%> (-26.2%)	⬇️
api/metric/kind_string.go	10.0% <0.0%> (-23.4%)	⬇️
api/metric/numberkind_string.go	16.6% <0.0%> (-16.7%)	⬇️