Fix MariaDb document issues

[msJinLei]

Description

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate ChangeLog.md file(s) has been updated:
  • For any service, the ChangeLog.md file can be found at src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md
  • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header -- no new version header should be added
• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
• For public API changes to cmdlets:
  • a cmdlet design review was approved for the changes in this repository (Microsoft internal only)
  • the markdown help files have been regenerated using the commands listed here

[isra-fel]

A small suggestion: we should use MariaDB in strings displayed to customer, because it's more formal. MariaDb should only be used internally. Otherwise it LGTM

[msJinLei]

A small suggestion: we should use MariaDB in strings displayed to customer, because it's more formal. MariaDb should only be used internally. Otherwise it LGTM

Your proposal make sense. However, currently we use MariaDb as the term of MariaDB in the Azure PowerShell

https://docs.microsoft.com/en-us/powershell/module/az.mariadb/?view=azps-4.7.0
https://docs.microsoft.com/en-us/powershell/module/az.mariadb/get-azmariadbconnectionstring?view=azps-4.7.0

We should change all of them to keep consistency.
Can you keep the current "MariaDb" temporarily?

[isra-fel]

As discussed, I will merge this PR and move the discussion for naming in another issue.