Do not use client entities not related with openapi.yaml tags

[lorddaedra]

Currently we use AppliedAddOnClient, GroupClient, AppliedCouponClient and WalletTransactionClient clients. It's completely okay as abstraction around collections but ideally we should not expose them as applied_add_ons, groups, applied_coupons and wallet_transactions properties of the Client instance. Or, at least, we can keep them for compatibility reasons but do not suggest to use by default.

Tasks:

1. Create aliases for all methods in AppliedAddOnClient, GroupClient, AppliedCouponClient and WalletTransactionClient clients

• "applyAddOn": AppliedAddOnClient.create -> AddOnClient.apply
• "findAllBillableMetricGroups": GroupClient.find_all -> BillableMetricClient.find_all_groups
• "applyCoupon": AppliedCouponClient.create -> CouponClient.apply
• "findAllAppliedCoupons': AppliedCouponClient.find_all -> CouponClient.find_all_applied
• "deleteAppliedCoupon": AppliedCouponClient.destroy -> CouponClient.delete_applied
• "createWalletTransaction": WalletTransactionClient.create -> WalletClient.create_transaction
• "findAllWalletTransactions": WalletTransactionClient.find_all -> WalletClient.find_all_transactions

2. Add deprecation comments to classes:

• AppliedAddOnClient,
• GroupClient,
• AppliedCouponClient and
• WalletTransactionClient.

3. Add pending deprecation warnings to callable cached properties in Client:

• applied_add_ons,
• groups,
• applied_coupons and
• wallet_transactions.

1-3 fixed in

• #134 - Do not use client entities not related with openapi.yaml tags #135

Note: algorithm for method name construction: operation name from OpenAPI spec file minus tag name.

After merging PR #135 and publishing new release:

4. Update Python docs to use these aliases
   Update Python docs lago-docs#172
5. Replace pending deprecation warning to deprecation warnings in Client:

• applied_add_ons,
• groups,
• applied_coupons and
• wallet_transactions.

6. Refactor tests to fix warnings