fix(http_requester): use host url as connections cache key

[kombucha]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	?
Related Issue	N/A
Need Doc update	no

Describe your change

Use the host.url, which should be unique, instead of the host.accept value, which in most cases is not unique, when caching the http client in the @connections instance variable of http_requester

What problem is this fixing?

Failing to do that, all hosts will actually use the same http client as the first one (assuming they share the same accept value). This prevents the retry strategy from working properly
For example:

1. you have host1, host2 & host3 configured. host1 is down.
2. you call algolia_client.indexes
3. transporter -> retry_strategy -> http_requester will try to request host1 and instantiate an http client with its url.
4. The request fails
5. There's a retry on host2, but http_requester.connections[host2.accept] will yield the same http client as host1!
6. All subsequent requests will fail despite the retry strategy