NPM Package Registry search API endpoint (#20280)

Close #20098, in the NPM registry API, implemented to match what's described by https://github.com/npm/registry/blob/master/docs/REGISTRY-API.md#get-v1search

Currently have only implemented the bare minimum to work with the [Unity Package Manager](https://docs.unity3d.com/Manual/upm-ui.html).

Co-authored-by: Jack Vine <[email protected]>
Co-authored-by: KN4CK3R <[email protected]>
Co-authored-by: Lunny Xiao <[email protected]>
Co-authored-by: wxiaoguang <[email protected]>

doc/packages/npm.en-us.md

@@ -127,6 +127,10 @@ npm dist-tag add [email protected] release
 
 The tag name must not be a valid version. All tag names which are parsable as a version are rejected.
 
+## Search packages
+
+The registry supports [searching](https://docs.npmjs.com/cli/v7/commands/npm-search/) but does not support special search qualifiers like `author:gitea`.
+
 ## Supported commands
 
 ```
@@ -136,4 +140,5 @@ npm publish
 npm unpublish
 npm dist-tag
 npm view
+npm search
 ```