feat(block storage): update the voluume backup guide

[OvhValentin]

What type of Pull Request is this?

• Update of existing guide(s)

Description

Refer to SK-2081

Mandatory information

The translations in this Pull Request have been done using:

• [ ] OVHcloud integrated translation LLM
• [ ] Systran
• [ ] Other tool (specify which tool was used)
• [x] This Pull Request didn't require any translation.

• This Pull Request can be merged as soon as possible.

• This Pull Request content should be replicated for the US OVHcloud documentation : YES/NO