[EPIC] Test/Enable Node.js 14 support for connectors

[dhmlau]

Similar to #3072

After loopbackio/loopback-datasource-juggler#1841 has landed to enable Node.js 14 support, the next step is to test and add support for Node.js 14.x for the connectors.

Acceptance Criteria

• Blog post on why we want to support Node.js 14 for loopback
  • Reference: https://strongloop.com/strongblog/lb3-entered-maintenance-mode/

For the following connectors, test locally on Node.js 14 and see if all tests passed.

• If yes, add Node.js 14 to CI
• If not, try to fix it for simple fixes. If you don't think you can fix it in a day, open a new issue to keep track of it.

Here is the list of connectors:

SQL connectors: #6020

• loopback-connector
• loopback-connector-mysql
• loopback-connector-postgresql
• loopback-connector-mssql
• loopback-connector-oracle
• loopback-connector-db2 (need to find out if ibm_db supports Node.js 14)

noSQL connectors: #6021

• loopback-connector-mongodb
• loopback-connector-couchdb2
• loopback-connector-cloudant
• loopback-connector-cassandra

service connectors: #6022

• loopback-connector-remote
• loopback-connector-rest
• loopback-connector-soap
• loopback-connector-jsonrpc
• loopback-connector-openapi