Add transport support to connect with an extension

[saratvemulapalli]

Transport Service with OpenSearch by default supports connecting to different nodes on the cluster.
Extend this mechanism to connect to an independent plugin running on the system.

TransportService connects to different nodes via DiscoveryNode.
We might have to implement something similar for a plugin.

• TransportService exposing an interface to connect to an extension
• Send a connection request to an extension
• Send a message to an extension
• Serialize/de-serialize bi-directional communication with an extension
• Manual testing
• Sanitize code and abstract out pieces of TransportService (to be merged to main)
• Integration tests

[saratvemulapalli]

Update: I was able to get OpenSearch to talk to a TCP server(extension) and receive a message.

[2022-03-01T18:14:25,891][INFO ][o.o.p.PluginsOrchestrator] [runTask-0] {runTask-0}{E3X_bXMeQWSqEM3JYCxhLw}{fYaYY3ayQXewn4u156BgjQ}{127.0.0.1}{127.0.0.1:9300}{dimr}{testattr=test, shard_indexing_pressure_enabled=true}
[2022-03-01T18:14:25,892][INFO ][o.o.t.TransportService   ] [runTask-0] connectToNode Connecting to node {node_g}{JfkfZZloTHCD1h133btYlw}{127.0.0.1}{127.0.0.1:65432}{dimr}
[2022-03-01T18:14:25,892][INFO ][o.o.t.ClusterConnectionManager] [runTask-0] connectToNode {node_g}{JfkfZZloTHCD1h133btYlw}{127.0.0.1}{127.0.0.1:65432}{dimr}
[2022-03-01T18:14:25,927][INFO ][o.o.p.PluginsOrchestrator] [runTask-0] ConnectTransportException[[][127.0.0.1:65432] connect_exception]; nested: AnnotatedSocketException[Connection reset by peer: /127.0.0.1:65432]; nested: SocketException[Connection reset by peer];
[2022-03-01T18:14:25,932][INFO ][o.o.t.TcpTransport       ] [runTask-0] readHeaderBuffer ES00001
[2022-03-01T18:14:25,934][INFO ][o.o.t.TcpTransport       ] [runTask-0] messageLength 10

[owaiskazi19]

Update: #2351 (comment)

[saratvemulapalli]

Closing this as the remaining items are anyway being tracked in #2228