Unify transport settings naming

[Tim-Brooks]

This commit updates our transport settings for 7.0. It generally takes a
few approaches. First, for normal transport settings, it usestransport.
instead of transport.tcp. Second, it uses transport.tcp, http.tcp,
or network.tcp for all settings that are proxies for OS level socket
settings. Third, it marks the network.tcp.connect_timeout setting for
removal. Network service level settings are only settings that apply to
both the http and transport modules. There is no connect timeout in
http. Fourth, it moves all the transport settings to a single class
TransportSettings similar to the HttpTransportSettings class.

This commit does not actually remove any settings. It just adds the new
renamed settings and adds todos for settings that will be deprecated.

[elasticmachine]

Pinging @elastic/es-distributed

[Tim-Brooks]

There is some inconsistency in our settings naming. Particularly as I think we want to move away from the tcp in some of our settings names (for non-socket option settings).

This PR is kind of a POC to see if there is agreement that this is the direction we want to head. If it is, I can open a meta issue with the follow plan:

1. Merge this into 7.0 and 6.x to add the replacement settings and mark the "for removal settings".
2. Update documentation for 7.0 to refer to the replacement settings.
3. Replace all "string" usage of the old settings with replacement settings.
4. On 7.0 deprecate the old settings.
5. On 8.0 delete the old settings.

These are the settings I would like to delete and their replacement:

D: transport.tcp.port
R: transport.port

D: transport.tcp.compress
R: transport.compress

D: transport.tcp_no_delay
R: transport.tcp.no_delay

D: transport.profiles._.tcp_no_delay
R: transport.profiles._.tcp.no_delay

D: transport.profiles._.tcp_keep_alive
R: transport.profiles._.tcp.keep_alive

D: transport.profiles._.reuse_address
R: transport.profiles._.tcp.reuse_address

D: transport.profiles._.send_buffer_size
R: transport.profiles._.tcp.send_buffer_size

D: transport.profiles._.receive_buffer_size
R: transport.profiles._.tcp.receive_buffer_size

D: http.tcp_no_delay
R: http.tcp.no_delay

D: network.tcp.connect_timeout
R: Nothing

[s1monw]

skimmed it, thanks for doing this!!

[Tim-Brooks]

run gradle build tests 2

[jasontedor]

Good change, thanks @tbrooks8.