fix: replace ClientSDK with Mina Signer in client-sdk.mdx

[barriebyron]

This PR started to fix a broken link because the Client SDK is now deprecated and is superseded by MinaSigner
So then the scope expanded to address quality opportunities(including case, consistency, style, capitalization, SNARK worker instances - see the Docs Style Guide for guidance, especially the Word List

• Replace the current Client SDK topic with a new Mina Signer topic that links to the repo with install and usage instructions
• Update the Node Operator FAQ topic to describe Mina Signer and mention deprecation, add description of zkApp, and update known errors

Mina friends! Please review updates to ensure I didn't inadvertently introduce technical inaccuracies

Questions? Please ask

As always, Mina docs contributions are most welcome (and much needed)

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Name	Status	Preview	Comments	Updated (UTC)
docs2	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 26, 2023 1:30pm

[barriebyron]

@MartinMinkov do we need a redirect here? and if so, how do redirects work?

[MartinMinkov]

@MartinMinkov do we need a redirect here? and if so, how do redirects work?

Yes, good catch! You can add one by adding the following code in our docusaurus.config.js file

{
  from: '/node-operators/client-sdk',
  to: '/node-operators/mina-signer',
},