[FEATURE] Custom user-agent

[scraly]

Description

For several needs it's necessary/usefull to add some custom informations in the user-agent.

The idea is to add, in the provider definition, a new field:

user_agent_append

(for example, choose another name if it is more relevant).

The idea is not to replace the user-agent, but to add some useful infirmations.

Potential Terraform Configuration

provider "ovh" {
  endpoint      = "ovh-eu"
  client_id     = "xxxxxxxxx"
  client_secret = "yyyyyyyyy"
  user_agent_append = "MyTool/2.0.7"
}