feat(docker): speed up docker build.

[appleboy]

As title. See the ref: https://semaphoreci.com/docs/docker/docker-layer-caching.html

before

Build time: 02:14 Link

after

Build time: 01:31 Link

[codecov-io]

Codecov Report

Merging #6159 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6159      +/-   ##
==========================================
- Coverage   38.85%   38.84%   -0.01%     
==========================================
  Files         354      354              
  Lines       50183    50183              
==========================================
- Hits        19497    19496       -1     
  Misses      27861    27861              
- Partials     2825     2826       +1

Impacted Files	Coverage Δ
modules/avatar/avatar.go	81.25% <0%> (-18.75%)	⬇️
models/repo_list.go	67.89% <0%> (+1.05%)	⬆️

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