feat: add subject relations

[everpcpc]

• related: feature: 条目-条目关联 #51

[codecov]

Codecov Report

Attention: Patch coverage is 96.34703% with 8 lines in your changes missing coverage. Please review.

Project coverage is 79.49%. Comparing base (7231de9) to head (27c5c3b).
Report is 115 commits behind head on master.

Files	Patch %	Lines
lib/graphql/types/subject.ts	95.03%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #672      +/-   ##
==========================================
- Coverage   81.98%   79.49%   -2.50%     
==========================================
  Files          69       76       +7     
  Lines        8554     9451     +897     
  Branches      405      424      +19     
==========================================
+ Hits         7013     7513     +500     
- Misses       1536     1933     +397     
  Partials        5        5              

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[trim21]

这个会造成 N+1 query 吧...

[everpcpc]

hmmm，graphql 不就是这个样子的吗

[trim21]

hmmm，graphql 不就是这个样子的吗

我意思是可以加在SubjectByIDQuery上面，感觉没必要加在Subject上？

[trim21]

写点测试