Azure functions proxies cannot proxy strings with slashes to the backend function without disabling local call.

Azure functions proxies cannot proxy strings with slashes to the backend function without disabling local call.

#### Repro steps

Create a proxy that proxies a string to a function
{
"proxies": {
"MyFunc/{arg0}": {
"matchCondition": {
"route": "/front/MyFunc/{arg0}",
"methods": [
"GET"
]
},
"backendUri": "http://%WEBSITE_HOSTNAME%/api/MyFunc/{arg0}"
}
}
}

invoke the urls:

http://%WEBSITE_HOSTNAME%/front/MyFunc/x%2Fy
http://%WEBSITE_HOSTNAME%/api/MyFunc/x%2Fy

The proxy will respond with 404 - not found. Backend responds with 200

#### Expected behavior

The proxy should return same result as when invoking the function directly

#### Actual behavior

The proxy will respond with 404 - not found.

#### Known workarounds

set the AZURE_FUNCTION_PROXY_DISABLE_LOCAL_CALL to true.

#### Related information

netcoreapp3.0