[R4R]add option to enable range query for tx indexer;add option to disable websocket

[unclezoro]

resolve issue #114

Description

more connection error between node and kafka should be taken into consideration

sarama didn't wrap tcp connection error. We need categorize them into retryable error so that downstream service cannot miss message.

Rationale

1. for now, tx_search API may take a very long time and huge memory to execute a range query. Have a DDOS issue.
2. We would like to have an option to disable WebSocket server when someone attack our dataseed through websocket, we can shut it down and restserver still works.

Example

➜  build git:(2f965c9) ✗ curl '127.0.0.1:26657/tx_search?query="tx.height>733"'
{
  "jsonrpc": "2.0",
  "id": "",
  "error": {
    "code": -32603,
    "message": "Internal error",
    "data": "range query is not supported by this node, detected invalid operators['>', '<', '<=', '>='] in the query statement"
  }
}%  

\u003e means >.

if disable websocket server:

Changes

Code tidy up

Preflight checks

• build passed (make build)
• tests passed (make test)

Already reviewed by

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Related issues

#114

[rickyyangz]

no need to find the operator, just print the query

[unclezoro]

updated

[rickyyangz]

on second thought, we may check strings.ContainsAny(s, "><") before we parse the query conditions.