fix(gatsby-source-mongodb): sanitize type of nodes to only contain alphanumeric chars and underscores (#7246)

Fixes: #7218 

(copied from issue)
This is due to the fact that `graphql` requires the node's `name` to match the `/^[_a-zA-Z][_a-zA-Z0-9]*$/` regex: 

https://github.com/graphql/graphql-js/blob/5fe39262a308df944a87cc85b225228e7556aaa4/src/utilities/assertValidName.js#L14

Author: michalczaplinski

packages/gatsby-source-mongodb/src/gatsby-node.js

@@ -83,7 +83,7 @@ function createNodes(
           parent: `__${collectionName}__`,
           children: [],
           internal: {
-            type: `mongodb${caps(dbName)}${caps(collectionName)}`,
+            type: `mongodb${sanitizeName(dbName)}${sanitizeName(collectionName)}`,
             content: JSON.stringify(item),
             contentDigest: crypto
               .createHash(`md5`)
@@ -129,8 +129,10 @@ function createNodes(
   })
 }
 
-function caps(s) {
-  return s.replace(/\b\w/g, l => l.toUpperCase())
+function sanitizeName(s) {
+  return s
+    .replace(/[^_a-zA-Z0-9]/, ``)
+    .replace(/\b\w/g, l => l.toUpperCase())
 }
 
 function getConnectionExtraParams(extraParams) {