[redis_proxy] Allow Multi-Key Commands in Redis Transactions

[dbarbosapn]

There's no functional difference currently in allowing multi-key commands to go through in Redis transactions. The way this will work is that they're sent to the server of the first key, and this server will handle any cross-slot errors, by returning ERR MOVED or ERR CROSSSLOT.

This PR fixes this gap which will allow Envoy customers to use DEL among other important commands within transactions.

Documentation was also updated, to reflect this and past changes (a miss from my side on previous PR, sorry 😛)

Risk Level: Low
Testing: ✅
Release Notes: ✅
Docs changes: ✅

Execution sample:

[KBaichoo]

/assign @weisisea

as codeowner, I'm not familiar enough with redis.

@dbarbosapn this needs a main merge for changelog.

[jmarantz]

needs main merge.

@dbarbosapn re your recent force-push, please read https://github.com/envoyproxy/envoy/blob/main/CONTRIBUTING.md and in particular the section https://github.com/envoyproxy/envoy/blob/main/CONTRIBUTING.md and this bullet:

• Once your PR is under review, please do not rebase it. If you rebase, you will need to force push to
  github, and github's user interface will force your reviewer to review the PR
  from scratch rather than simply look at your latest changes. It's much easier to review
  new commits and/or merges. We squash rebase the final merged commit so the number of commits
  you have in the PR don't matter. Again once your PR is assigned a reviewer, unless you need to fix DCO
  please do not force push. If you need to pull recent changes you can run

branch=$(git status|head -1|cut -f3 -d\ )
git checkout main
git pull
git checkout "$branch"
git merge main

/wait

[dbarbosapn]

needs main merge.

@dbarbosapn re your recent force-push, please read https://github.com/envoyproxy/envoy/blob/main/CONTRIBUTING.md and in particular the section https://github.com/envoyproxy/envoy/blob/main/CONTRIBUTING.md and this bullet:

• Once your PR is under review, please do not rebase it. If you rebase, you will need to force push to
  github, and github's user interface will force your reviewer to review the PR
  from scratch rather than simply look at your latest changes. It's much easier to review
  new commits and/or merges. We squash rebase the final merged commit so the number of commits
  you have in the PR don't matter. Again once your PR is assigned a reviewer, unless you need to fix DCO
  please do not force push. If you need to pull recent changes you can run

branch=$(git status|head -1|cut -f3 -d\ )
git checkout main
git pull
git checkout "$branch"
git merge main

/wait

It was to fix DCO 😄 I fixed changelog conflicts using the GitHub UI, it said "Sign Off and Commit", commit showed verified but DCO was claiming it was not, it was red 😄 So I had to rebase unfortunately

I don't know if it's because I enabled the beta merge experience UI 🤔

[dbarbosapn]

Hey @mattklein123 , @weisisea kind ping 🙇

[mattklein123]

LGTM please merge main.

/wait

[dbarbosapn]

Done. Thanks @mattklein123 🙇