Add mongo storage adapter

[mahendraHegde]

to provide more flexibility in storage options, need to add mongoDB as a storage adapter.

it should implement the Storage interface

node-idempotency/packages/storage/src/types.ts

Lines 1 to 11 in 21d260a

	export interface StorageAdapter {
	setIfNotExists: (
	key: string,
	val: string,
	{ ttl }?: { ttl?: number },
	) => Promise<boolean>;
	set: (key: string, val: string, { ttl }: { ttl?: number }) => Promise<void>;
	get: (key: string) => Promise<string | undefined>;
	connect?: () => Promise<void>;
	disconnect?: () => Promise<void>;
	}

steps:

1. add a new package similar to storage-adapter-redis
2. implement Storage with mongo native driver(refer below PR)
3. add tests

ref: #16
no need to provide enum based instantiation in shared repo, to reduce the bundle size, users will install the package and provide storageAdapter directly.