Update LoopBack 3 status to end-of-life (EOL)

[achrinza]

This issue is to keep a consolidated list of pull requests to update the LoopBack 3 status from Maintenance LTS to End-of-Life (EOL).

• [ ] eslint-config-loopback
• [x] generator-loopback (https://github.com/strongloop/generator-loopback/pull/420)
• [x] gulp-loopback-sdk-angular (https://github.com/strongloop/gulp-loopback-sdk-angular/pull/24)
• [x] grunt-loopback-sdk-angular (https://github.com/strongloop/grunt-loopback-sdk-angular/pull/40)
• [ ] icars-server
• [x] loopback-next (https://github.com/strongloop/loopback-next/pull/6908) (TODO: #6969)
• [x] loopback (https://github.com/strongloop/loopback/pull/4343)
• [ ] loopback-api-definition
• [x] loopback-boot (https://github.com/strongloop/loopback-boot/pull/308)
• [x] loopback-cli (https://github.com/strongloop/loopback-cli/pull/102)
• [ ] loopback-component-oauth2
• [ ] loopback-component-explorer
• [ ] loopback-component-passport
• [ ] loopback-component-push
• [x] loopback-connector-remote (https://github.com/strongloop/loopback-connector-remote/pull/106)
• [x] loopback-context (https://github.com/strongloop/loopback-context/pull/56)
• [x] loopback-datasource-juggler(https://github.com/strongloop/loopback-datasource-juggler/pull/1888)
• [ ] loopback-example-facade
• [x] loopback-filters (https://github.com/strongloop/loopback-filters/pull/37)
• [ ] loopback-getting-started
• [ ] loopback-getting-started-intermediate
• [ ] loopback-multitenancy
• [ ] loopback-multitenant-poc
• [ ] loopback-phase
• [ ] loopback-sdk-angular-cli
• [ ] loopback-soap
• [ ] loopback-swagger
• [ ] loopback-utils
• [ ] loopback-workspace
• [x] loopback.io (https://github.com/strongloop/loopback.io/pull/1125, https://github.com/strongloop/loopback.io/pull/1156)
• [ ] poc-loopback-multitenancy
• [ ] strong-remoting

Put a notice about LB3's EOL on the following pages.

• [ ] https://github.com/strongloop/loopback-next/tree/master/packages/booter-lb3app
• [ ] https://github.com/strongloop/loopback-next/tree/master/examples/lb3-application
• [ ] https://loopback.io/doc/en/lb4/migration-overview.html
• [ ] https://loopback.io/doc/en/lb4/migration-mounting-lb3app.html
• [x] https://loopback.io/doc/en/lb3/index.html