Migrate connector repos into monorepo

Nessuno ha ancora preso questa issue.

This issue is to track the feasibility of migration the connector repos into this monorepo.

**Problem statement**

The connectors are in separate repos, which results in...

1. Inconsistent automated maintenance and CI workflows (i.e. dependency/vuln. management, code/commit linting, CLA/DCO)
2. Disparate issue trackers (harder to keep track of connector-specific issues)
3. Non-integrated CI testing (i.e. integration tests are not executed on changes within the connector repo)

**Potential concerns**

1. **Slower CI build times** - This concern was raised when this repo was utilising Travis CI, which had slow a VM spin-up duration, and rather limited co-current actions. With GitHub Actions, this concern is potentially mitigated.
2. **Maxing out CI minutes** - This was an issue with Travis CI where there was a quota on build times. This is not an issue with GitHub Actions which has unlimited minutes for public repos.
3. **Loss of commit history** - `lerna import --preserve-commit` will preserve the relative commit history, and retain the original commit authors and committers.
4. **Linux-only testing** - GitHub Actions only supports containers/services with `ubuntu-*` images. Currently, the CI pipeline for most connectors are hosted under `cis-jenkins.swg-devops.com`, which isn't currently publicly-accessible AFAIK.

**Connectors**

These are the connectors that are officially maintained:

- [ ] loopback-connector-mysql
- [ ] loopback-connector-postgresql
- [ ] loopback-connector-mongodb
- [ ] loopback-connector-rest
- [ ] loopback-connector-mssql
- [ ] loopback-connector-soap
- [ ] loopback-connector-oracle
- [ ] loopback-connector-cloudant
- [ ] loopback-connector-cassandra
- [ ] loopback-connector-couchdb2
- [ ] loopback-connector-db2
- [ ] loopback-ibmdb
- [ ] loopback-connector-dashdb
- [ ] loopback-connector-grpc
- [ ] loopback-connector-kv-redis
- [ ] loopback-connector-openapi
- [ ] loopback-connector-sqlite3
- [ ] loopback-connector-elastic-search
- [ ] loopback-connector-redis
- [ ] loopback-connector-kv-extreme-scal
- [ ] strong-soap

Inizia esaminando i repository dei connector elencati e i relativi workflow CI esistenti, quindi valuta le problematiche di migrazione descritte nell’issue, inclusi la cronologia dei commit e gli ambienti di test. Il lavoro è completo quando sono stati prodotti una decisione di fattibilità e un piano di migrazione che affrontino l’elenco dei connector, l’integrazione CI e i rischi indicati.

Scritto dal modello di indicizzazione a partire dal testo della issue.