Add public tags and documentation in the error and config-loader packages

Part of #7688

Signed-off-by: Fredrik Adelöw <freben@gmail.com>

packages/errors/api-report.md

@@ -14,7 +14,7 @@ export class AuthenticationError extends CustomErrorBase {}
 // @public
 export class ConflictError extends CustomErrorBase {}
 
-// @public (undocumented)
+// @public
 export class CustomErrorBase extends Error {
   constructor(message?: string, cause?: Error | unknown);
   // (undocumented)

packages/errors/src/errors/CustomErrorBase.ts

@@ -16,7 +16,21 @@
 
 import { isError } from './assertion';
 
-/** @public */
+/**
+ * A base class that custom Error classes can inherit from.
+ *
+ * @public
+ * @example
+ *```ts
+ * class MyCustomError extends CustomErrorBase {}
+ *
+ * const e = new MyCustomError('Some message', cause);
+ * // e.name === 'MyCustomError'
+ * // e.message === 'Some message'
+ * // e.cause === cause
+ * // e.stack is set if the runtime supports it
+ * ```
+ */
 export class CustomErrorBase extends Error {
   readonly cause?: Error;