Fix relative path in uri

[Kukks]

When the base url has a subpath, and the relative url has a leading "/", the subpath of the base url is ignored. Initially ran into this in #9904, and @kiminuo showed me the correct usage. Since I was only testing with the wabisabi client, it all worked fine. Now, I was testing with the full wasabi client ans the api calls in WasabiClient all have a leading "/", causing the same issue. This PR removes all leading "/" in HttpClient Send requests.

[kiminuo]

The changes look correct to me. I can run WW with these changes too, so it looks OK.

[lontivero]

cACK. Just FTR, it is also possible to use ./ with the exact same result as the intended.

> let baseUri = Uri "http://mydomain/api/"
- let relativeUri = Uri("./path/subpath?q=query", UriKind.Relative)
- let uri = Uri(baseUri, relativeUri);;
val baseUri: Uri = http://mydomain/api/
val relativeUri: Uri = ./path/subpath?q=query
val uri: Uri = http://mydomain/api/path/subpath?q=query

> let relativeUri = Uri("path/subpath?q=query", UriKind.Relative)
- let uri = Uri(baseUri, relativeUri);;
val relativeUri: Uri = path/subpath?q=query
val uri: Uri = http://mydomain/api/path/subpath?q=query

[lontivero]

We need to verify the server side changes work okay. It looks like a completely safe change to me.

[kiminuo]

@adamPetho Can we check easily that the server side changes are OK? Deploy to testnet? I'm not sure.

[adamPetho]

Can we check easily that the server side changes are OK? Deploy to testnet?

I think that's the easiest way to test it. It works fine on RegTest.

[kiminuo]

Can we check easily that the server side changes are OK? Deploy to testnet?

I think that's the easiest way to test it. It works fine on RegTest.

And can anybody do it then?

[molnard]

And can anybody do it then?

After the merge, yes. As a fundamental test, RegTest is enough - for being able to merge - so I will do it.