While I was fixing a documentation issue (#22007), I looked at the code and discovered that we actually never read what the user entered as a `readonly` parameter when he creates an azure repository.
So if someone sends:
```
PUT _snapshot/my_backup4
{
"type": "azure",
"settings": {
"account": "my_account2",
"location_mode": "primary_only",
"readonly": true
}
}
```
The repository is not actually defined as `readonly`.
It's caused by the fact we are always overwriting `readonly`setting based on `location_mode`.
If a user sets it to `primary_only`, `readonly` is forced to `false`.
If a user sets it to `primary_then_secondary`, `readonly` is forced to `false`.
If a user sets it to `secondary_only`, `readonly` is forced to `false`.
Note that with this change, a user can force a `secondary_only` repository to `readonly: false` which will lead him to an error later on when we check the repository as per definition in Azure, a secondary repository is not writable.
Another option could have been to detect this mismatch and throw an exception in that case. Note sure it is worth writing more code though.
Closes#22053.
8b0df47381