Add redirects for docs.substrate.com --> docs.polkadot.com to solve error 404s fix

[RemyLeBerre]

Summary
This PR solves a variety of error 404 links that users would get when being redirected from docs.substrate.io to docs.polkadot.com

This PR solves the following 404 errors listed below and has redirected them to working links which can be seen in the commits of the PR

https://docs.polkadot.com/develop/development-pathways/#client-side-development
https://docs.polkadot.com/develop/parachains/get-started/intro-polkadot-sdk/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/connect-to-relay-chain/acquire-a-testnet-slot/
https://docs.polkadot.com/develop/development-pathways/
https://docs.polkadot.com/develop/parachains/get-started/intro-polkadot-sdk/
https://docs.polkadot.com/develop/parachains/get-started
https://docs.polkadot.com/develop/parachains/get-started/install-polkadot-sdk/#linux
https://docs.polkadot.com/develop/parachains/get-started/install-polkadot-sdk/#macos
https://docs.polkadot.com/develop/parachains/get-started/install-polkadot-sdk/
https://docs.polkadot.com/develop/parachains/get-started/install-polkadot-sdk/#verifying-installation
https://docs.polkadot.com/develop/parachains/get-started/install-polkadot-sdk/#windows-wsl
https://docs.polkadot.com/develop/parachains/get-started/install-polkadot-sdk/
https://docs.polkadot.com/develop/parachains/get-started/intro-polkadot-sdk/
https://docs.polkadot.com/develop/parachains/get-started
https://docs.polkadot.com/develop/development-pathways/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/local-chain/launch-a-local-solochain/
https://docs.polkadot.com/develop/parachains/get-started/intro-polkadot-sdk/
https://docs.polkadot.com/develop/parachains/get-started/
https://docs.polkadot.com/develop/parachains/customize-parachain/benchmarking/
https://docs.polkadot.com/develop/parachain/testing
https://docs.polkadot.com/develop/parachain/testing
https://docs.polkadot.com/develop/parachains/customize-parachain/pallet-testing/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/local-chain/spin-your-nodes/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/local-chain/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/local-chain/launch-a-local-solochain/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/local-chain/connect-multiple-nodes/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/local-chain/upgrade-a-running-network/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/local-chain/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/connect-to-relay-chain/acquire-a-testnet-slot/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/connect-to-relay-chain/prepare-parachain/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/connect-to-relay-chain/prepare-relay-chain/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/connect-to-relay-chain/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/local-chain/launch-a-local-solochain/#interact-with-the-node
https://docs.polkadot.com/develop/parachain/testing
https://docs.polkadot.com/develop/parachains/get-started/build-custom-parachains/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/local-chain/spin-your-nodes/
https://docs.polkadot.com/tutorials/polkadot-sdk/parachains/connect-to-relay-chain/acquire-a-testnet-slot/
https://docs.polkadot.com/develop/parachains/customize-parachain/pallet-testing/
https://docs.polkadot.com/develop/parachains/customize-parachain/pallet-testing/
https://docs.polkadot.com/develop/parachains/customize-parachain/benchmarking/
https://docs.polkadot.com/develop/parachains/customize-parachain/benchmarking/#benchmark-testing-and-weight
https://docs.polkadot.com/develop/parachains/get-started/intro-polkadot-sdk/

cc @nprt @kianenigma

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[RemyLeBerre]

Note: I noticed I missed 301! 'force redirect' commands on some 3 of the links, this ensures docs.polkadot.com gets prioritisation when there are 2 active URLs

I have opened a PR to solve this: https://github.com/polkadot-developers/substrate-docs/pull/2192/files