docs: Rename host options to endpoint

[ktff]

Ref. #1775

This PR address the core of the #1775 and renames host options to endpoint where applicable. Old names are still usable, while the documentation is updated to use endpoint.

This also changes:

• datadog_logs sink endpoint option into address since the option fits address definition and not endpoint. (Edit: reverted)
• papertrail sink endpoint option into address for the same reason. (Edit: reverted)
• pulsar sink address option into endpoint since that option fits endpoint definition.

[jszwedko]

I think what you have here is good, but just offering that another option for consolidating to just use endpoint would be to use:

• tcp:// for the datadog one; this may make it easier to allow use of their HTTPS endpoint later
• syslog+tcp:// for the papertrail one; similarly we could allow use of their HTTPS endpoint later. Edit it looks like they also support udp as well as tcp without TLS too, though I'm not sure we do (https://help.papertrailapp.com/kb/configuration/encrypting-remote-syslog-with-tls-ssl/).

The downside is the schemes would be required even though only one is current supported; though I don't think this is different from the pulsar sink and HTTP based sinks probably only really allow for https for the cloud-based services.

[bruceg]

I don't see why the datadog_logs and papertrail sinks are being moved away from the endpoint setting. Do they not also use an URL, as evidenced by the use of UriSerde?

[bruceg]

Looks fine except for the endpoint => address question.

[ktff]

why the datadog_logs and papertrail sinks are being moved away from the endpoint setting

datadog_logs and papertrail sinks only use host and port part of UriSerde, which corresponds to address in other sinks, for example socket sink.

Now, that is current situation, but with future upgrades mentioned by @jszwedko it makes more sense to retain them as endpoints.

The downside is the schemes would be required even though only one is current supported

We can supply/assume a default scheme if none is specified.

[jszwedko]

Apologies, didn't get back to this as quickly as I'd like. This looks good to me. I like your idea of a "default scheme".