Fix syntax for `getindexinfo` params in help examples #22430

txindex without quotes:

$ curl --user myusername --data-binary '{"jsonrpc": "1.0", "id": "curltest", "method": "getindexinfo", "params": [txindex]}' -H 'content-type: text/plain;' http://127.0.0.1:18333/



{"result":null,"error":{"code":-32700,"message":"Parse error"},"id":null}

txindex with quotes:

$ curl --user myusername --data-binary '{"jsonrpc": "1.0", "id": "curltest", "method": "getindexinfo", "params": ["txindex"]}' -H 'content-type: text/plain;' http://127.0.0.1:18333/



{"result":{"txindex":{"synced":true,"best_block_height":2032943}},"error":null,"id":"curltest"}

ACK e0aa8de

tested:

$ ./src/bitcoin-cli -signet help getindexinfo
...
Examples:
> bitcoin-cli getindexinfo
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id": "curltest", "method": "getindexinfo", "params": []}' -H 'content-type: text/plain;' http://127.0.0.1:8332/
> bitcoin-cli getindexinfo txindex
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id": "curltest", "method": "getindexinfo", "params": ["txindex"]}' -H 'content-type: text/plain;' http://127.0.0.1:8332/