Bootstrap: Is it possible to specify a specific ssh key rather than default id_rsa?

I was reading this paragraph:

Ansible commands are executed on the Ansible Controller from unprivileged account alice. 
This user has an SSH key pair stored in ~/.ssh/id_rsa or has its SSH key available in the 
SSH Agent. An administrator account with the same name will be created on the remote 
host during the bootstrap process.

https://docs.debops.org/en/master/debops-playbooks/guides/getting-started.html?highlight=ansible_ssh_host

I see the default behavior is to use the ~/.ssh/id_rsa however is it possible to override this and specify a specific key e.g. ~/.ssh/ubuntu instead? That way I can share a key among specific hosts and not all of them. And also not share my ~/.ssh/id_rsa if I don't want to.

I'm also not that clear on why the authorized_keys of both alice@ and root@ contains so many entries, maybe all my keys in .ssh? Shouldn't it just contain the one and also can it be specified exactly?

I'm a bit confused by what is happening basically. Please can you explain or point to the relevant docs which I couldn't find on the first pass.

Also, is there any documentation about what steps bootstrap.yml and common.yml actually do? I find I'm flying a little blind as I don't know what is actually happening on my servers lol.

Many thanks.

-Mike

Start with the linked getting-started guide and inspect bootstrap.yml and common.yml to trace SSH key selection and the authorized_keys entries mentioned in the issue. Document whether a specific key can be selected, why the entries are present, and what those playbooks do, with examples that let readers verify the behavior.