feat: add ability to check for multiple default ssh key locations

[a-dubs]

Since Ubuntu 24.04 LTS and newer, the default location for ssh keys is
~/.ssh/id_ed25519 instead of ~/.ssh/id_rsa. Thus, when no ssh key
path is specified, this commit changes pycloudlib to check for an
existing ssh key at either ~/.ssh/id_ed25519 or ~/.ssh/id_rsa.

Fixes GH #341

---

Testing of changes

Testing id_ed25519 can be found

1. made sure no key exists at ~/.ssh/id_rsa
2. created new key at ~/.ssh/id_ed25519
3. removed public_key_path and private_key_path from [oci] config in my pycloudlib.toml config file
4. ran the oracle example script: python3 examples/oracle.py
5. made sure the following line showed up in the log (was one of the first few lines logged):

DEBUG:pycloudlib.cloud.OCI:using SSH pubkey: /home/a-dubs/.ssh/id_ed25519.pub

Testing error is raised when neither default key is found

1. Removed keys at ~/.ssh/id_ed25519
2. ran the oracle example script: python3 examples/oracle.py
3. Ensured error stating the following was thrown:

pycloudlib.errors.PycloudlibError: No public key path provided and no key found in default locations: '~/.ssh/id_rsa.pub' or '~/.ssh/id_ed25519.pub'

Testing error is raised when key from config does not exist:

1. set public_key_path in [oci] config in my pycloudlib.toml config file to be ~/.ssh/nonexistant-key.pub
2. ran the oracle example script: python3 examples/oracle.py
3. Ensured error stating the following was thrown:

pycloudlib.errors.PycloudlibError: Provided public key path '/home/a-dubs/.ssh/oracle-ipv6-testing.pub1' does not exist

[a-dubs]

putting this into draft until i fix tests.

[a-dubs]

Also, should i add new unit tests that verify the functionality of the added changes? @holmanb (tag you're it)

[holmanb]

Also, should i add new unit tests that verify the functionality of the added changes? @holmanb (tag you're it)

Pycloudlib's test coverage is unfortunately very light on tests, but in this case the feature being tested is something that a user would immediately notice if it isn't working.

I'm honestly not sure whether it would be worth the effort in this case to write and maintain a test given the infrequency of changes to this part of the code and the immediate feedback that we would receive.

What do you think?

[holmanb]

This turns __init__() mostly into a key-handling function. I would prefer a helper method _get_ssh_keys()[1] to contain this logic and get called from __init__()

[1] maybe a better name, I didn't put any thought into that one

[a-dubs]

Haha agreed! Way too much going on there. And would allow for actually unit testing that (if so desired)

[a-dubs]

Also, should i add new unit tests that verify the functionality of the added changes? @holmanb (tag you're it)

Pycloudlib's test coverage is unfortunately very light on tests, but in this case the feature being tested is something that a user would immediately notice if it isn't working.

I'm honestly not sure whether it would be worth the effort in this case to write and maintain a test given the infrequency of changes to this part of the code and the immediate feedback that we would receive.

What do you think?

Let me go fix the existing unit tests that this change broke, and see if this change gets inherently tested that way. If not, it should be sufficient to just test the helper function that I'll create encapsulating this functionality.

[a-dubs]

@holmanb ready for re-review!