[BE] Default version for Create DB cluster

User story:

• When I Manage the list of versions available to be used in the DB Creation process I need to be able to select the default versions

UI/UX:
TBD

Acceptance criteria

• user able to see the recommended version from percona

• the recommended version is default by default

• User able to redefine the default

• When the new recommended version arrived the default is not changed if it was specified manually

• When the new recommended version arrived the default changed to it if a user didn't specify a different version already as the default

Out of scope:
TBD

Suggested implementation:

• **Reuse dependency graph endpoint implemented in https://jira.percona.com/browse/PMM-7485. 

  • This endpoint should include boolean field `default` as part of service info.

• Store default version per kubernetes cluster.

  • Create new endpoint for each DB type.

• Questionable things:

  • if default version is not set in pmm-managed settings yet set default: true next to recommended service in response. ?

  • if default version is not present in version service response, use recommended service as default

How to test:

1. Open DBaaS page

2. Select Kubernetes cluster

3. Open version management modal

4. Check that you see all DB versions

5. Check that you see recommended DB version

6. Check that you see latest recommended version as default version

7. Select default DB version

8. Save changes

9. Refresh the page

10. Check that default version is set

Details:
TBD

Questions:

• What if default version is not present for some kubernetes clusters? - Use the recommended version