refactor: rename package remote to package etcd

[Reasno]

ETCD is only one of the remote config implementations. It should not be called package remote.

Also core should not import stuff from etcd. It unnecessarily bloats build size.

[codecov]

Codecov Report

Merging #175 (2c198be) into master (7d7f997) will increase coverage by 0.18%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #175      +/-   ##
==========================================
+ Coverage   80.23%   80.41%   +0.18%     
==========================================
  Files          91       91              
  Lines        3273     3273              
==========================================
+ Hits         2626     2632       +6     
+ Misses        471      466       -5     
+ Partials      176      175       -1     

Impacted Files	Coverage Δ
c.go	76.55% <ø> (+1.04%)	⬆️
config/remote/etcd/etcd.go	86.20% <100.00%> (ø)
config/watcher/file.go	62.79% <0.00%> (+4.65%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7d7f997...2c198be. Read the comment docs.