Update crutch.rb to allow crutch inter-dependency with efficiency

[akshay58538]

Adds support for passing all crutches into a crutch definition, to be able to form a chain of crutches such that a field can depend and load only what it needs, instead of loading multiple objects at times, which might not all be required always.

Earlier:

class MyIndex

    crutch :my_large_crutch do |models|
        model_rel1_ids = models.map { |m| m.rel1_id }
        rel1_objs = <Load objects of Rel1 from Mongo>
        rel2_ids = rel1_objs.map{ |r| r.rel2_id }
        rel2_objs  = <Load objects of Rel2 from Mongo>
        ..... Relations can go any nested levels
        data = {}
        data[:rel1_objs] = <hash_of rel1_objs>
        data[:rel2_objs] = <hash_of rel2_objs>
        data
    end

    field :field_belongs_to_rel1_obj # <also ends up loading rel2 objects in case of partial update>
    field :field_belongs_to_rel2_obj
end

Now:

class MyIndex

    crutch :my_rel1_objs do |models|
         model_rel1_ids = models.map { |m| m.rel1_id }
        rel1_objs = <Load objects of Rel1 from Mongo>
        <hash of rel1_objs>
    end

    crutch :my_rel2_objs do |_, crutches|
         rel1_objs = crutches.my_rel1_objs
         rel2_ids = rel1_objs.map{ |r| r.rel2_id }
        rel2_objs  = <Load objects of Rel2 from Mongo>
        <hash of rel2_objs>
    end

    field :field_belongs_to_rel1_obj # <now can depend only on my_rel1_objs crutch, avoiding loading of rel2 objects, in case of a partial update>
    field :field_belongs_to_rel2_obj
end

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• [x] The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• [ ] Wrote good commit messages.
• [ ] Commit message starts with [Fix #issue-number] (if the related issue exists).
• [x] Feature branch is up-to-date with master (if not - rebase it).
• [x] Squashed related commits together.
• [ ] Added tests.
• [ ] Added an entry to the changelog if the new code introduces user-observable changes. See changelog entry format for details.