TT-8942 Change default RPC pool size (#5030)

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## Description
Default RPC pool size is set to 20 and because of the relatively heavy
CPU and Memory footprint of the RPC connections in the MDCB model this
can cause issues where either the gateways or MDCB fail on load cause by
scaling events or component failure at MDCB side.

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## Related Issue

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https://tyktech.atlassian.net/browse/TT-8942
## Motivation and Context

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https://tyktech.atlassian.net/browse/TT-8942
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## Types of changes

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- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Refactoring or add test (improvements in base code or adds test
coverage to functionality)

## Checklist

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- [ ] I ensured that the documentation is up to date
- [ ] I explained why this PR updates go.mod in detail with reasoning
why it's required
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explained why

config/config.go

@@ -312,7 +312,7 @@ type SlaveOptionsConfig struct {
 	// The maximum time in seconds that a RPC ping can last.
 	PingTimeout int `json:"ping_timeout"`
 
-	// The number of RPC connections in the pool. Basically it creates a set of connections that you can re-use as needed.
+	// The number of RPC connections in the pool. Basically it creates a set of connections that you can re-use as needed. Defaults to 5.
 	RPCPoolSize int `json:"rpc_pool_size"`
 
 	// You can use this to set a period for which the Gateway will check if there are changes in keys that must be synchronized. If this value is not set then it will default to 10 seconds.

rpc/rpc_client.go

@@ -253,7 +253,7 @@ func Connect(connConfig Config, suppressRegister bool, dispatcherFuncs map[strin
 
 	clientSingleton.Conns = values.Config().RPCPoolSize
 	if clientSingleton.Conns == 0 {
-		clientSingleton.Conns = 20
+		clientSingleton.Conns = 5
 	}
 
 	clientSingleton.Dial = func(addr string) (conn net.Conn, err error) {