Bringing back 1 x filters

[zajko]

Rationale As a user of sidecar that's used to consume 1.x style sse events I want to be still able to listen to events after 2.0 changes. Notes The goal of this effort is to recreate the sse filter endpoints from 1.x. For now the endpoints will be satureated with 2.x style SSE events, but before release we need to translate them to 1.x format.

Work done Sidecars SSE server has 3 more endpoints:

• /main -> transmits ApiVersion, FinalitySignature and Shutdown events
• /deploys -> transmits ApiVersion, TransactionAccepted and Shutdown events
• /sigs -> transmits ApiVersion, BlockAdded, TransactionProcessed, TransactionExpired, Fault, Step and Shutdown events

[rafal-ch]

Plase consider adding the new flag to the example configs and perhaps a readme file.