title: How to add custom search_field Django admin
body: <p>I want to create a new search field box with my on filters, and add to the django admin:</p>
  
  <p>admin.py</p>
  
  <pre><code>  from django.contrib import admin
  from .models import Aluno, Data
  from .relatorio import salvarRelatorio
  
  
  
  class AdminAluno(admin.ModelAdmin):
      list_editable = ['is_active',]
      list_display = ['first_name', 'matricula', 'is_active','cpf', 'cargo', 'date_joined','image_tag'] ##mostra esses campos
      search_fields = ['first_name', 'matricula'] ## campos q pesquise
      exclude = ['password']
  
  class AdminData(admin.ModelAdmin):
      list_display = ['aluno__first_name','data_entrada', 'hora_entrada', 'hora_saida', 'descricao'] ##mostra esses campos
      search_fields = ['aluno__first_name', 'matricula', 'data_entrada'] ## campos q pesquise
      actions = [salvarRelatorio]
  
  
  admin.site.register(Aluno, AdminAluno)
  admin.site.register(Data, AdminData)
  </code></pre>
  
  <p>I want to create a extra search field to filter with data_entrada__gte and data_entrada__lte.</p>