docs: Add token-2022 extension docs and JS examples (#3457)

* token-js: Add examples for all extensions

* docs: Add token-2022 extensions guide for JS

* Address feedback

* Fix extension

Author: joncinque

docs/src/token-2022.md

@@ -108,7 +108,7 @@ program, that creates new token accounts for either Token or Token-2022.
 To get started with Token-2022:
 
 - [Install the Solana Tools](https://docs.solana.com/cli/install-solana-cli-tools)
-- [Extension Guide](token-2022/extensions.md)
+- [Extension Guide](token-2022/extensions.mdx)
 - [Wallet Guide](token-2022/wallet.md)
 - [On-Chain Program Guide](token-2022/onchain.md)