Add contained_db field to mssql db secret backend

[benashz]

In addition the following updates were made

• run mssql database secret backend connection tests against a local
  mssql docker container
• factor out db backend types to constants
• update canonical list of db backend types to include all supported
  types
• add ability to skip db tests globally or based on the db engine type

Dependency updates:

• terraform-plugin-sdk/v2 to v2.10.0
• vault/api v1.3.0
• vault/sdk v0.3.1-0.20211214161113-fcc5f22bea02
• vault v1.2.1-0.20211214161113-fcc5f22bea02

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Closes #1237

Release note for CHANGELOG:

Output from acceptance testing:

 make dev testacc TESTARGS='-v -test.run TestAccDatabaseSecretBackendConnection_mssql'
==> Checking that code complies with gofmt requirements...
go build -o terraform-provider-vault
mv terraform-provider-vault ~/.terraform.d/plugins/
TF_ACC=1 go test $(go list ./...) -v -v -test.run TestAccDatabaseSecretBackendConnection_mssql -timeout 20m

[...]

=== RUN   TestAccDatabaseSecretBackendConnection_mssql
--- PASS: TestAccDatabaseSecretBackendConnection_mssql (13.97s)
PASS
ok      github.com/hashicorp/terraform-provider-vault/vault     14.782s