Replace Authorities with Validators throughout

[Clay-Mysten]

In the Validator Onboarding Kickoff meeting last week, we settled upon renaming Authorities as Validators throughout our technical contents. This affects:
docs.sui.io
Sui white paper
And the nuances described here:
https://docs.sui.io/learn/sui-compared#authorities-vs-validatorsminers

I am undertaking the Dev Portal docs first and have asked the white paper team if they want help with that document too. Will include members here for a decision and action.

[Clay-Mysten]

Here are all of the references in the Sui repository:

authorit-sui-refs.txt

Sam, a lot of this is in the code. Are we updating those references now? If not, it could get confusing to have validators in the text and authorities in the code and code samples. Talks to me.

[Clay-Mysten]

Here is a problematic example:

sui/doc/src/contribute/observability.md:2022-03-05T01:35:03.385294Z DEBUG test_move_call_args_linter_command:process_tx{tx_digest=t#7e5f08ab09ec80e3372c101c5858c96965a25326c21af27ab7774d1f7bd40848}: sui_core::authority: Checked locks and found mutable objects num_mutable_objects=2

I assume we would not change sui_core::authority to sui_core::validator now. But:

1. When and by whom?
2. Won't it confuse users to see authority everywhere in the code and output?

[Clay-Mysten]

And so on:

sui/doc/src/contribute/observability.md:From the example above, we can see that `process_tx` is a span that covers handling the initial transaction request, and "Checked locks" is a single log message within the transaction handling method in the authority.
sui/doc/src/contribute/observability.md:| process_tx              | Gateway, Authority | Send transaction request, get back 2f+1 signatures and make certificate        |
sui/doc/src/contribute/observability.md:| process_cert            | Gateway, Authority | Send certificate to authorities to execute transaction                         |
sui/doc/src/contribute/observability.md:| cert_check_signature    | Authority          | Check certificate signatures                                                   |
sui/doc/src/contribute/observability.md:| process_cert_inner      | Authority          | Inner function to process certificates in authority                            |
sui/doc/src/contribute/observability.md:| fetch_objects           | Authority          | Read objects from database                                                     |
sui/doc/src/contribute/observability.md:| tx_execute_to_effects   | Authority          | Execute Move call and create effects       

[Clay-Mysten]

Let's also move authorities.md into a learn/architecture subdirectory while renaming to validators.md per:
#1363