feat(fsaas): new guide about external provisionner

[OvhValentin]

What type of Pull Request is this?

• New guide(s)
• Index categories update

Description

Refer to SK-2657

Mandatory information

The translations in this Pull Request have been done using:

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

• This Pull Request can be merged as soon as possible.
• This Pull Request shouldn't be merged before: YYYY-MM-DD

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