Migrate to docs.substrate.io throughout

[nuke-web3]

• All crates homepage = "https://substrate.io" (this is almost all of the file changes)
  • It is unclear to me how this will affect crates.io and publishing there (if at all)
• Fix all comments/doc links to use new site (a few were 404s previously)
  • Note: link to specific docs include v3 in the URL, for new versions of the docs we need to replace this manually (unless I am missing a redirect @imadarai @sacha-l ?)
• Omits the template, this is in Move template to homepage = "https://substrate.io/" , correct links #10006

(#10017 created in this PR)

[athei]

Why not linking flat substrate.io there? Should be the better landing page when just wanting to learn what it is.

[bkchr]

Why not linking flat substrate.io there? Should be the better landing page when just wanting to learn what it is.

Yeah. This field is named homepage, so it should link to substrate.io

[gilescope]

LGTM - needs cargo fmt

[imadarai]

@nukemandan
Does this header gets applied to all the rust-docs or just substrate?

I'd like to remove Google Analytics and update the script with Simple Analytics (cookie-less), but will need the exact links where it's being used.

[nuke-web3]

Moved to homepage = "https://substrate.io" throughout.

I ran cargo +nightly fmt with today's toolchain. This had a code format change in:

• client/network/src/service.rs
• primitives/keystore/src/testing.rs

This right?

[gilescope]

Try doing a cargo fmt with 2021-09-01 nightly (which seems to be the nightly that it's using, though confusingly there seem to be two nightly versions installed).

[nuke-web3]

My sincere apologies: I did not see the A7 tag here the bot added! Does this need to be reverted? What Polkadot PR is needed that triggered this?

At least this I figure: paritytech/polkadot#4076

Also, what should be noted in the next release? Should this be in the change log at all?
I am not sure if there is any ramification on crates.io for instance cc @gnunicorn .

[gilescope]

I don't know why it added that flag. The polkadot companion build was fine - everything was green before merge so you should be good (esp as this is just docs change).