Add metadata about internal db connection in common_data

[Anish9901]

Fixes #3292

Technical details

Using postgres as an internal db returns:

{
  "internal_database": {
    "type": "postgres",
    "user": "mathesar",
    "host": "localhost",
    "port": "5432",
    "database": "mathesar_django"
  }
}

Using sqlite as an internal db returns:

{
  "internal_database": {
    "type": "sqlite"
  }
}

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• I added or updated documentation (if applicable).
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  visible errors.

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[seancolsen]

I tried this out and it gives me what I need. Thanks @Anish9901!

I'll leave it to @mathemancer to merge in case he wants to do additional backend review.

[mathemancer]

Looks good to me as well. Nice work, @Anish9901 .