docs: clarify type constraints for collections in locals

HCL2 locals don't have type constraints, and the map syntax is interpreted as
an object. So users may need to explictly convert to map for some functions.

The `convert` function documentation was missing the required type constructor
parameter for collections.

website/content/docs/job-specification/hcl2/functions/conversion/convert.mdx

@@ -35,18 +35,18 @@ All other values will produce an error.
 false
 > convert(false, string)
 "false"
-> convert(["a", "b", 3], list)
+> convert(["a", "b", 3], list(string))
 [
   "a",
   "b",
   "3",
 ]
-> convert(["c", "b", "b"], set)
+> convert(["c", "b", "b"], set(string))
 [
   "b",
   "c",
 ]
-> convert({"a" = "foo", "b" = true}, map)
+> convert({"a" = "foo", "b" = true}, map(string))
 {
   "a" = "foo"
   "b" = "true"

website/content/docs/job-specification/hcl2/locals.mdx

@@ -12,8 +12,9 @@ description: >-
 Local values assign a name to an expression, that can then be used multiple
 times within a folder.
 
-If [variables](/docs/job-specification/hcl2/variables) are analogous to function arguments then
-_local values_ are comparable to a function's local variables.
+If [variables](/docs/job-specification/hcl2/variables) are analogous to
+function arguments then _local values_ are comparable to a function's local
+variables.
 
 ## Examples
 
@@ -24,6 +25,10 @@ Local values are defined in `locals` blocks:
 locals {
   default_name_prefix = "${var.project_name}-web"
   name_prefix         = "${var.name_prefix != "" ? var.name_prefix : local.default_name_prefix}"
+
+  # unlike variables, locals don't have type constraints, so if you use
+  # functions that take maps but not objects, you may need to convert them
+  number_of_ports = length(convert({"www" = "80"}, map(string)))
 }
 
 # Local values can be interpolated elsewhere using the "local." prefix.