Refactor e2e test and examples

[altafan]

This fixes the integration test for the v1 version of the daemon.

It also refactors the buy/sell trading example scripts so that they can be used within the e2e test and standalone.

[what-the-diff[bot]]

PR Summary

• Moved example to separate file The example has been moved to its own file for better organization.
• Added BuyExample() and SellExample() functions New functions have been added to be used by other examples, simplifying code and enabling greater reusability.
• Removed unnecessary code related to btcec and elementsutil This simplifies the example by not requiring keypairs, signatures, etc.
• Implemented explorerSvc for better abstraction Now using an interface, making it easier to switch service providers if needed.
• Created utils.go for additional utility functions Functions for initializing services, getting test coins, and working with tdexv2 API calls are now defined in this new file.
• Removed trade package and added end-to-end test examples Improves testing capabilities by incorporating test examples from tdex-daemon/cmd/tdexd.
• Updated market precision and trading fees Adjusted market precision for regtest network and set trading fees for the market.
• Replaced static price with price feeder Uses a price feeder to open the market instead of setting a static price manually. Aims to restore price feed support for the v2 protocol in the future.