Fix and improve suggestion experience in Formula (elastic#19)

* ✨ Revisit documentation and suggestions

* 👌 Integrated feedback

x-pack/plugins/lens/public/indexpattern_datasource/operations/definitions/calculations/counter_rate.tsx

@@ -129,11 +129,10 @@ Calculates the rate of an ever increasing counter. This function will only yield
 If the value does get smaller, it will interpret this as a counter reset. To get most precise results, \`counter_rate\` should be calculated on the \`max\` of a field.
 
 This calculation will be done separately for separate series defined by filters or top values dimensions.
+It uses the current interval when used in Formula.
 
 Example: Visualize the rate of bytes received over time by a memcached server:
-\`\`\`
-counter_rate(max(memcached.stats.read.bytes))
-\`\`\`
+${'`counter_rate(max(memcached.stats.read.bytes))`'}
       `,
     }),
   },

x-pack/plugins/lens/public/indexpattern_datasource/operations/definitions/calculations/cumulative_sum.tsx

@@ -123,9 +123,7 @@ Calculates the cumulative sum of a metric over time, adding all previous values
 This calculation will be done separately for separate series defined by filters or top values dimensions.
 
 Example: Visualize the received bytes accumulated over time:
-\`\`\`
-cumulative_sum(sum(bytes))
-\`\`\`
+${'`cumulative_sum(sum(bytes))`'}
       `,
     }),
   },

x-pack/plugins/lens/public/indexpattern_datasource/operations/definitions/calculations/differences.tsx

@@ -121,9 +121,7 @@ Differences requires the data to be sequential. If your data is empty when using
 This calculation will be done separately for separate series defined by filters or top values dimensions.
 
 Example: Visualize the change in bytes received over time:
-\`\`\`
-differences(sum(bytes))
-\`\`\`
+${'`differences(sum(bytes))`'}
       `,
     }),
   },

x-pack/plugins/lens/public/indexpattern_datasource/operations/definitions/calculations/moving_average.tsx

@@ -150,9 +150,7 @@ This calculation will be done separately for separate series defined by filters
 Takes a named parameter \`window\` which specifies how many last values to include in the average calculation for the current value.
 
 Example: Smooth a line of measurements:
-\`\`\`
-moving_average(sum(bytes), window=5)
-\`\`\`
+${'`moving_average(sum(bytes), window=5)`'}
       `,
       values: {
         defaultValue: WINDOW_DEFAULT_VALUE,

x-pack/plugins/lens/public/indexpattern_datasource/operations/definitions/cardinality.tsx

@@ -112,21 +112,17 @@ export const cardinalityOperation: OperationDefinition<CardinalityIndexPatternCo
   documentation: {
     section: 'elasticsearch',
     signature: i18n.translate('xpack.lens.indexPattern.cardinality.signature', {
-      defaultMessage: 'field: string, [kql]?: string, [lucene]?: string',
+      defaultMessage: 'field: string',
     }),
     description: i18n.translate('xpack.lens.indexPattern.cardinality.documentation', {
       defaultMessage: `
 Calculates the number of unique values of a specified field. Works for number, string, date and boolean values.
 
 Example: Calculate the number of different products:
-\`\`\`
-unique_count(product.name)
-\`\`\`
+${'`unique_count(product.name)`'}
 
 Example: Calculate the number of different products from the "clothes" group:
-\`\`\`
-unique_count(product.name, kql="product.group=clothes")
-\`\`\`
+${"`unique_count(product.name, kql='product.group=clothes')`"}
       `,
     }),
   },

x-pack/plugins/lens/public/indexpattern_datasource/operations/definitions/count.tsx

@@ -91,22 +91,16 @@ export const countOperation: OperationDefinition<CountIndexPatternColumn, 'field
   filterable: true,
   documentation: {
     section: 'elasticsearch',
-    signature: i18n.translate('xpack.lens.indexPattern.count.signature', {
-      defaultMessage: '[kql]?: string, [lucene]?: string',
-    }),
+    signature: '',
     description: i18n.translate('xpack.lens.indexPattern.count.documentation', {
       defaultMessage: `
 Calculates the number of documents.
 
 Example: Calculate the number of documents: 
-\`\`\`
-count()
-\`\`\`
+${'`count()`'}
 
 Example: Calculate the number of documents matching a certain filter:
-\`\`\`
-count(kql="price > 500")
-\`\`\`
+${"`count(kql='price > 500')`"}
       `,
     }),
   },