add JSON-RPC endpoint playground links

[0xshikhar]

Description

The main changes involve adding a new "Try this endpoint" button/link to several API endpoint sections. This allows users to easily test out the endpoints in an interactive playground.

Specific changes:
Added playground links to the following endpoints:

• eth_syncing
• eth_coinbase
• eth_chainId
• eth_mining
• eth_hashrate
• eth_gasPrice
• eth_accounts
• eth_blockNumber
• eth_getBalance
• eth_getStorageAt
• eth_getBlockByHash
• eth_getBlockByNumber
• eth_getTransactionByHash
• eth_getTransactionByBlockHashAndIndex
• eth_getTransactionByBlockNumberAndIndex
• eth_getUncleByBlockHashAndIndex
• eth_getUncleByBlockNumberAndIndex

Added playground button SVG markup:

Related Issue

Issue #13410

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