feat(sc-57427): Support Opportunities API

[kamilpavlicko]

closes ticket: https://app.shortcut.com/chartmogul/story/57427/support-opportunities-resource-ruby-client?vc_group_by=day&ct_workflow=all&cf_workflow=500105879

API document: https://www.notion.so/chartmogul/API-endpoints-for-Opportunities-a92323514bf44f89ad2f97ae30cee7f0#6f09cc7a71bc40e69ef65d8d0342d230

Background

1. Create a opportunity

customer = ChartMogul::Customer.retrieve('cus_3819e09a-50a2-11ee-ada7-9fcf71cd4580')
customer.create_opportunity(
  ....
)

ChartMogul::Opportunity.create(data)

2. Get all opportunities

customer = ChartMogul::Customer.retrieve('cus_3819e09a-50a2-11ee-ada7-9fcf71cd4580')
customer.opportunities

ChartMogul::Opportunity.all(customer_uuid: customer_uuid)

3. Get an opportunity

opportunities = ChartMogul::Opportunity.retrieve('opportunity_uuid')

4. Update an opportunity

updated_opportunity = ChartMogul::Opportunity.update(data)

5. Delete an opportunity

ChartMogul::Opportunity.delete('opportunity_uuid') 

[shortcut-integration]

This pull request has been linked to Shortcut Story #57427: Support Opportunities resource - Ruby client.

[codeclimate]

Code Climate has analyzed commit 2e5b695 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 98.5% (0.0% change).

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