[4.x] Laravel 7

Drop test collections correctly

Make functions and tests compatible with laravel 7

Date serialization changes
Laravel 7 uses a new date serialization format when using the toArray or toJson method on Eloquent models. To format dates for serialization, the framework now uses Carbon's toJSON method, which produces an ISO-8601
https://laravel.com/docs/7.x/upgrade#date-serialization
 laravel_7_comptability

$model->getOriginal() was moved to getRawOriginal method See https://laravel.com/docs/7.x/upgrade#factory-types

Bump dependencies for laravel 7

Remove php 7.1 which is EOL.

Remove phpcov, it's not compatible and suggested to be installed with phar instead of composer, see sebastianbergmann/phpcov#96

[4.x] Apply fixes from StyleCI

[4.x] Remove shouldUseCollections function

Remove shouldUseCollections function which checks Laravel version > 5.3, it was introduced to support version 5.3 in https://github.com/jenssegers/laravel-mongodb/pull/925

[4.x] Remove embeds relations

Remove unneeded test, builds are failing Error: Call to a member function pluck() on array

Removed embedded relations
Updated documenation
Added changelog

[4.x] Add changelog, code of conduct, contributing

Added changelog, code of conduct, contributing.

[fix] Make newPivotQuery function public

Laravel versions starting from 6 are all  6.x

PR https://github.com/laravel/framework/pull/31677 made newPivotQuery function public and that's the reason why builds are failing.

Fix getDefaultDatabaseName to handle +srv URLs.

Fixes #1977, fixes #1861

Fix a typo

`belongsToMany` operation is imporing the `Model` with a typo. Fixed it.

[refactor] tests

[fix] default database detection from dsn

Refactored default database function which detects based on db config or tries to detect it from dsn

Add MIT license

There is no currently license file, PR https://github.com/jenssegers/laravel-mongodb/pull/1780 was pushed to develop branch.

[fix] Correct import class for DB in Queue

PR https://github.com/jenssegers/laravel-mongodb/pull/1851 had incorrect class import, we need to define correct path, see issue https://github.com/jenssegers/laravel-mongodb/issues/1868

[Fix] Format exception to string in failed jobs

[Updated PR#1534] UTCDateTime conversion now includes milliseconds