Docs on using tipped transactions

[amaury1093]

Part of the TX working group.

Summary

Add docs on what tipped transactions are, and how to use them.

Problem Definition

In #10208 we added a Tips middleware. There are currently no docs.

Proposal

This docs change be thought as 2 pieces, which can be done in 2 PRs.

• docs: Add docs for SIGN_MODE_DIRECT_AUX #11858 on https://docs.cosmos.network/master/core/transactions.html, add new & updated sign modes;
  • DIRECT_AUX
  • LEGACY_AMINO_JSON ref: feat: Add fee.{payer,granter} and tip fields to StdSignDoc #10348 (review)
• docs: Add transaction tips documentation #11426 A new page on Core Concepts called "Transaction Tips".
  • Subsections can be:
    • Use cases
    • Tipper and Fee payer sign modes
    • Usage
      • Programmatic usage (AuxTxBuilder)
      • CLI usage

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