chore: refactor module patch handling in Instrumentation class

This refactors how module patch handlers are loaded and the
Instrumentation class file. There is now a PatcherRegistry that is
a little smarter than the `_patches` object before it.

The main change is that we now use RITM's internals:true option
so that our `onRequire` hook is called with module sub-paths. This will
allow #3657 to hook both "mongodb" and "mongodb/lib/cmap/connection_pool.js",
and avoid a RITM bug where "mongodb" &
"mongodb/lib/cmap/connection_pool" (no extension, indicating a
"sub-module") don't work together.

Benefits and other changes:
- With the smarter "PatcherRegistry" the module name can be used in
  `disableInstrumentations` to disable any patchers for that module.
  E.g. `disableInstrumentations=next` will disable all four
  `next`-related patchers.
- A custom "lambda" name is now usable to disable the Lambda instr,
  FWIW.
- (Note: we *could* also add custom disableInstrumentations keys for
  other modules, e.g. perhaps "aws-sdk" for all those.)
- Some edge cases with the (rare, and undocumented) `config.addPatch`
  config var have been cleaned up.
- Loading of the lambda-handler has been refactored a bit to no longer
  need to know internal details of the instrumentation module.

Refs: #3657
Closes: #2992

docs/agent-api.asciidoc

@@ -810,6 +810,10 @@ apm.addPatch('timers', (exports, agent, { version, enabled }) => {
 apm.addPatch('timers', './timer-patch')
 ----
 
+This and the other "Patch"-related API methods should be called *before*
+starting the APM agent. Changes after the agent has started and relevant
+modules have been `require`d can have surprising caching behavior.
+
 [[apm-remove-patch]]
 ==== `apm.removePatch(modules, handler)`
 

docs/configuration.asciidoc

@@ -962,7 +962,7 @@ The `sanitizeFieldNames` will redact any matched _field names_.  If you wish to
 * *Type:* Array of strings
 * *Env:* `ELASTIC_APM_DISABLE_INSTRUMENTATIONS`
 
-Array or comma-separated string of modules to disable instrumentation for.
+Array or comma-separated string of module names for which to disable instrumentation.
 When instrumentation is disabled for a module,
 no spans will be collected for that module.
 
@@ -971,15 +971,15 @@ Example using options object:
 [source,js]
 ----
 require('elastic-apm-node').start({
-  disableInstrumentations: ['graphql', 'redis']
+  disableInstrumentations: ['graphql', '@redis/client']
 })
 ----
 
 Example using environment variable:
 
 [source,bash]
 ----
-ELASTIC_APM_DISABLE_INSTRUMENTATIONS=graphql,redis
+ELASTIC_APM_DISABLE_INSTRUMENTATIONS=graphql,@redis/client
 ----
 
 For an always up-to-date list of modules for which instrumentation can be disabled,

index.d.ts

@@ -381,6 +381,7 @@ declare namespace apm {
   type PatchHandler = (exports: any, agent: Agent, options: PatchOptions) => any;
 
   interface PatchOptions {
+    name: string;
     version: string | undefined;
     enabled: boolean;
   }