graphqlbackend: update throttled to use Ctx stores

[keegancsmith]

It seems we were using a weird version of throttled which I don't think was actually based on the v2 series correctly. This updates us to the latest version and moves us away from the removed struct GCRARateLimiter and the deprecated interface GCRAStore.

I came across this while attempting to update deps and getting failing compiles.

Test Plan: we have unit tests for this, so CI.

[keegancsmith]

@jhchabran what is the black magic one needs so that backcompat tests work after dependency updates?

[jhchabran]

@keegancsmith here you go :) https://sourcegraph.com/notebooks/Tm90ZWJvb2s6MzA1Mw==

[keegancsmith]

rebased and added a commit which fixed the lint errors. Doing that also made me realise the the RateLimit struct was unused, so I just removed it.

[github-actions]

The backport to 5.1 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-5.1 5.1
# Navigate to the new working tree
cd .worktrees/backport-5.1
# Create a new branch
git switch --create backport-54748-to-5.1
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 c390e4bacb1e233aea179840f8ce0e5e56695527
# Push it to GitHub
git push --set-upstream origin backport-54748-to-5.1
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-5.1

Then, create a pull request where the base branch is 5.1 and the compare/head branch is backport-54748-to-5.1.