feature(@nestjs/terminus) Add health check for mongoose ODM

[nartc]

• Refactor for HealthIndicator and AbstractDatabaseHealthIndicator abstract classes
• Make MongooseHealtIndicator and DatabaseHealthIndicator (subject to rename to TypeOrm) to extends AbstractDatabaseHealthIndicator for abstract pingDb and the underlying connection
• Add mongoose and @nestjs/mongoose to peerDependencies and optionalDependencies
• Add @types/mongoose to devDependencies
• Add Unit Test (With Livio help. Thanks!)
• Add new sample app 001-mongoose-app to demo MongooseHealthIndicator

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #35

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[BrunnerLivio]

Great! Thanks a lot for your time, really clean PR :)