Fix template flag for extensions

[isaacroldan]

WHY are these changes introduced?

The flavour selection logic was comparing the provided flag with the template human name instead of the value (Rust vs rust)
Fixes #996

WHAT is this pull request doing?

• Compare the provided template flag with the value of the supported flavours
• Add some tests to prevent this in the future

How to test your changes?

pnpm shopify app generate extension --type payment_customization --template rust should work now

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
• I've made sure that any changes to dev or deploy have been reflected in the internal flowchart.

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	68.26% (-0.23% 🔻)	3555/5208
🟡	Branches	64.07% (-0.12% 🔻)	1457/2274
🟡	Functions	66.64% (-0.15% 🔻)	909/1364
🟡	Lines	69.04% (-0.29% 🔻)	3385/4903

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🔴	... / order_discounts.ts	50% (-50% 🔻)	100%	0% (-100% 🔻)	50% (-50% 🔻)
🟡	... / extension.ts	60.81% (-20.27% 🔻)	51.61% (-15.05% 🔻)	58.82% (-17.65% 🔻)	60.81% (-20.27% 🔻)

Test suite run success

887 tests passing in 459 suites.

Report generated by 🧪jest coverage report action from b37ace4

[github-actions]

Benchmark report

The following table contains a summary of the startup time for all commands.

Status	Command	Baseline	Current	Diff
🟢	app build	1280 ms	1208 ms	-5.63 %
🟢	app deploy	1341 ms	1239 ms	-7.61 %
🟢	app dev	1341 ms	1259 ms	-6.11 %
🟢	app env pull	1271 ms	1209 ms	-4.88 %
🟢	app env show	1262 ms	1212 ms	-3.96 %
🟢	app generate extension	1298 ms	1214 ms	-6.47 %
🟢	app generate schema	1278 ms	1215 ms	-4.93 %
🟢	app info	1328 ms	1252 ms	-5.72 %
🟢	app scaffold extension	1297 ms	1231 ms	-5.09 %
🟢	theme check	1256 ms	1164 ms	-7.32 %
🟢	theme delete	1254 ms	1183 ms	-5.66 %
🟢	theme dev	1283 ms	1206 ms	-6 %
🟢	theme help-old	1289 ms	1180 ms	-8.46 %
🟢	theme info	1266 ms	1170 ms	-7.58 %
🟢	theme init	1250 ms	1178 ms	-5.76 %
🟢	theme language-server	1251 ms	1180 ms	-5.68 %
🟢	theme list	1240 ms	1169 ms	-5.73 %
🟢	theme open	1258 ms	1175 ms	-6.6 %
🟢	theme package	1275 ms	1171 ms	-8.16 %
🟢	theme publish	1260 ms	1170 ms	-7.14 %
🟢	theme pull	1265 ms	1173 ms	-7.27 %
🟢	theme push	1260 ms	1170 ms	-7.14 %
🟢	theme share	1265 ms	1167 ms	-7.75 %
🟢	webhook trigger	1252 ms	1180 ms	-5.75 %