2382 - API changes for project page front

[amiedes]

(!) To be merged after #2383

Closes #2382

✌️ What does this PR do?

Implements a mechanism so the different plugins can attach custom information to any Gobierto Model. Specifically for this case, modifies the JSON returned by the GobiertoPlans project API so it includes information about budget, human resources and indicators.

🔍 How should this be manually tested?

You can edit this project in staging and see the API response in http:https://talavan.gobify.net/planes/gobierto_plans/api/plan_projects/17/2198

Does this PR changes any configuration file?

No

📖 Does this PR require updating the documentation?

• new site configuration variable?
• new site template?
• new module/submodule settings?
• significant changes in some feature - Delegated to Document and improve how to add behavior to Gobierto with plugins #2394

[codecov-io]

Codecov Report

Merging #2393 into master will increase coverage by 0.09%.
The diff coverage is 75.92%.

@@            Coverage Diff             @@
##           master    #2393      +/-   ##
==========================================
+ Coverage   81.25%   81.35%   +0.09%     
==========================================
  Files         687      693       +6     
  Lines       17942    18094     +152     
==========================================
+ Hits        14579    14720     +141     
- Misses       3363     3374      +11

Impacted Files	Coverage Δ
lib/budgets_seeder.rb	0% <0%> (ø)
...corators/gobierto_plans/category_term_decorator.rb	98.38% <100%> (+0.08%)	⬆️
...lans/category_term_decorator_budgets_attachment.rb	100% <100%> (ø)
...s/gobierto_common/custom_field_functions/budget.rb	96.55% <100%> (ø)
...egory_term_decorator_human_resources_attachment.rb	100% <100%> (ø)
...ugin/lib/custom_fields_data_grid_plugin/railtie.rb	100% <100%> (ø)	⬆️
app/models/gobierto_plans/node.rb	87.5% <100%> (+0.65%)	⬆️
...s/category_term_decorator_indicators_attachment.rb	100% <100%> (ø)
... and 6 more

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[amiedes]

This is ready. @ferblape I'll update this PR and ping you for a review once #2383 is merged.