[API] Implement functions - estimateRelayerFee

[just-a-node]

Problem

Implement the functions:

• estimateRelayerFee

Impact

Integrators will use this function to estimate the relayer fee that goes into xcall.

Proposed Solution

estimateRelayerFee should:

• Fetch native token conversion rates for origin/destination and relayer fee estimates from Gelato
• Fetch hardcoded gas limits from chaindata
• Apply a configurable relayer buffer (20% default) on top of the estimated fee
• Accept price inputs for native token prices (e.g. if both origin and destination native prices are supplied, there is no need to fetch the conversion rate, saving an external call)
• Accept priceIn to select whether the estimate should be denominated in native asset or USD (this is so relayer fee can be paid in transacting asset)

Acceptance Criteria

• [ ] estimateRelayerFee returns the relayer fee estimate denominated in either the native asset or in USD

Open questions

• Can we supply any asset into the Gelato conversion rate? If we can denominate the relayer fee in the transactingAsset, this saves integrators the step of converting USD -> transactingAsset amount.

[prathmeshkhandelwal1]

Created helpers like GelatoService which above method will use internally.

[prathmeshkhandelwal1]

Need to add retry logic, Ques is do we do it in separate method or in httpClient? cc: @just-a-node

[prathmeshkhandelwal1]

Writing tests