Add user registration

[dsychin]

User registration only

Example query

mutation {
  registerAccount(input: {email: "test@example.com", password: "helloworld"}) {
    __typename
    ... on LoginResult {
      accessToken
    }
  }
}

Contributes to #17

[codecov-commenter]

Codecov Report

Merging #41 (51f029e) into main (48c6b27) will increase coverage by 2.04%. The diff coverage is 75.47%.

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
+ Coverage   39.02%   41.06%   +2.04%     
==========================================
  Files           6        8       +2     
  Lines         287      375      +88     
==========================================
+ Hits          112      154      +42     
- Misses        155      195      +40     
- Partials       20       26       +6     

Impacted Files	Coverage Δ
pkg/model/model.go	80.00% <ø> (ø)
pkg/service/job.go	0.00% <ø> (ø)
pkg/graph/schema.resolvers.go	72.72% <66.66%> (+13.90%)	:arrow_up:
pkg/service/user.go	76.59% <76.59%> (ø)

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