feat: implement ohttp gateway middleware

[Harshdev098]

part of #941

added ohttp gateway middleware in payjoin-services.

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[zealsham]

ThankS for working on this @Harshdev098. Ideally we would want this middleware to be written with axum so it would fit in with the rest of the middlwares we plan to add, @spacebear21 this is correct right ?

[spacebear21]

we would want this middleware to be written with axum so it would fit in with the rest of the middlwares we plan to add

Yes exactly. The gateway should be an axum middleware written mostly from scratch similar to @zealsham's ongoing work in #1296. Duplication could also be reduced by first making the helper utils (encapsulate_xxx, decapsulate_xxx, constants...) pub in the ohttp-relay crate and reusing them in payjoin-service.

[Harshdev098]

okay will use axum in the middleware and update you!