chore(backend): remove wallet address middleware

[mkurapov]

Changes proposed in this pull request

To finalize the standardization of Open Payments route errors in backend, this PR removes walletAddressMiddleware. The benefits:

• We now handle all possible errors properly in the openPaymentsServerErrorMiddleware (i.e. we don't use ctx.throw at all in other places)
• walletAddressUrl is determined as an inline-middleware per route, meaning the complex logic walletAddressMiddleware can be removed
• We don't need to fetch the walletAddress until each route needs it. This is nice for a few reasons:
  • we can control whether a route will poll (or not) the wallet address creation at the ASE (i.e. we can choose whether a route will call walletAddressService.getOrPollByUrl or just getByUrl)
  • we can eliminate a request to get the wallet address before other checks are ran (like token introspection, http signature middleware, Open Api validation, etc)

Context

Completion of backend changes for #1905

Checklist

• [x] Related issues linked using fixes #number
• [x] Tests added/updated
• [ ] Documentation added
• [ ] Make sure that all checks pass
• [ ] Bruno collection updated

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