Support graphiql variables query param

[jgray7019]

WHY are these changes introduced?

Part of https://github.com/Shopify/shopify-dev/issues/50532

Following up from #3345 where the query param support was implemented it would also be great it if we supported the variables query param that the GraphiQL explorer also supports. Example: https://graphql.github.io/swapi-graphql/?variables=variables

WHAT is this pull request doing?

Forwards the variables query param if present

How to test your changes?

• Run app dev
• Press g
• Nothing should change
• Add ?variables=test to the url in the browser and refresh
• There should be a new tab with the variables
• query params should still work

Measuring impact

How do we know this change was effective? Please choose one:

• n/a - this doesn't need measurement, e.g. a linting rule or a bug-fix
• Existing analytics will cater for this addition
• PR includes analytics changes to measure impact

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	75.29% (+0.07% 🔼)	8841/11742
🟡	Branches	70.56% (+0.09% 🔼)	4290/6080
🟡	Functions	75.19% (+0.04% 🔼)	2315/3079
🟡	Lines	75.84% (+0.07% 🔼)	8358/11021

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🟢	... / app-event-watcher.ts	93.83% (-1.23% 🔻)	86.49%	90.48%	98.61%
🔴	... / server.ts	1.25% (-0.03% 🔻)	0%	0%	1.32% (-0.04% 🔻)
🔴	... / api.ts	56.29% (-3.01% 🔻)	43.59% (-1.53% 🔻)	57.5% (-2.5% 🔻)	57.59% (-3.14% 🔻)

Test suite run success

1994 tests passing in 902 suites.

Report generated by 🧪jest coverage report action from 2d92db7