fix: enforce weight precision to 1 decimal (#2749)

## About the changes
According to our docs, we only support up to 1 decimal place for
weights. This is to use integers to represent the percentages (we divide
them by 10) and supporting more decimals results in bad maths due to
floating point arithmetics.

This PRs adds Frontend and Backend validations to enforce this
restriction

Closes #2222

## Discussion points
Should we reconsider supporting more decimal places, that door remains
open, but for now we'll just adhere to our documentation because that
change would require some development.

frontend/src/component/feature/FeatureView/FeatureVariants/FeatureEnvironmentVariants/EnvironmentVariantModal/EnvironmentVariantModal.tsx

@@ -274,6 +274,7 @@ export const EnvironmentVariantModal = ({
     const isValidPercentage = (percentage: string) => {
         if (!customPercentage) return true;
         if (percentage === '') return false;
+        if (percentage.match(/\.[0-9]{2,}$/)) return false;
 
         const percentageNumber = Number(percentage);
         return percentageNumber >= 0 && percentageNumber <= 100;

src/lib/schema/feature-schema.test.ts

@@ -70,6 +70,56 @@ test('should allow weightType=fix', () => {
     expect(value).toEqual(toggle);
 });
 
+test('should not allow weightType=fix with floats', () => {
+    const toggle = {
+        name: 'app.name',
+        type: 'release',
+        project: 'default',
+        enabled: false,
+        impressionData: false,
+        stale: false,
+        archived: false,
+        strategies: [{ name: 'default' }],
+        variants: [
+            {
+                name: 'variant-a',
+                weight: 1.5,
+                weightType: 'fix',
+                stickiness: 'default',
+            },
+        ],
+    };
+
+    const { error } = featureSchema.validate(toggle);
+    expect(error.details[0].message).toEqual('Weight only supports 1 decimal');
+});
+
+test('should not allow weightType=fix with more than 1000', () => {
+    const toggle = {
+        name: 'app.name',
+        type: 'release',
+        project: 'default',
+        enabled: false,
+        impressionData: false,
+        stale: false,
+        archived: false,
+        strategies: [{ name: 'default' }],
+        variants: [
+            {
+                name: 'variant-a',
+                weight: 1001,
+                weightType: 'fix',
+                stickiness: 'default',
+            },
+        ],
+    };
+
+    const { error } = featureSchema.validate(toggle);
+    expect(error.details[0].message).toEqual(
+        '"variants[0].weight" must be less than or equal to 1000',
+    );
+});
+
 test('should disallow weightType=unknown', () => {
     const toggle = {
         name: 'app.name',

src/lib/schema/feature-schema.ts

@@ -50,7 +50,13 @@ export const variantValueSchema = joi
 
 export const variantsSchema = joi.object().keys({
     name: nameType,
-    weight: joi.number().min(0).max(1000).required(),
+    weight: joi
+        .number()
+        .integer()
+        .message('Weight only supports 1 decimal')
+        .min(0)
+        .max(1000)
+        .required(),
     weightType: joi.string().valid('variable', 'fix').default('variable'),
     payload: joi
         .object()