Make sendDatexViaHTTPChannel() asynchronous

[asbng]

datex-core-js-legacy/network/datex-http-channel.ts

Line 16 in 0e3224c

fetch(origin + "/datex-http", {

is not prefixed with the await keyword. The sendDatexViaHTTPChannel function should be marked as async.

[jonasstrehle]

We should probably return the fetch promise without marking the method as async. In theory there is no need to await the result of fetch, but if we want to await the send we can do that at the specific point in code