Add System Truststore Fallback

[gl-johnson]

Desired Outcome

When the .conjurrc config cert_file property points to an invalid CA (or self-signed) cert, the API should still attempt to use the system truststore to verify the SSL connection.

Implemented Changes

Append system trusted CA certs to the SSL context even when a cert path is given.

Connected Issue/Story

CyberArk internal issue link: ONYX-24957 This PR should also address cyberark-conjur-cli#209

Definition of Done

At least 1 todo must be completed in the sections below for the PR to be merged.

Changelog

• [x] The CHANGELOG has been updated, or
• [ ] This PR does not include user-facing changes and doesn't require a CHANGELOG update

Test coverage

• [x] This PR includes new unit and integration tests to go with the code changes, or
• [ ] The changes in this PR do not require tests

Documentation

• [ ] Docs (e.g. READMEs) were updated in this PR
• [ ] A follow-up issue to update official docs has been filed here: [insert issue ID]()
• [x] This PR does not require updating any documentation

Behavior

• [ ] This PR changes product behavior and has been reviewed by a PO, or
• [x] These changes are part of a larger initiative that will be reviewed later, or
• [ ] No behavior was changed with this PR

Security

• [x] Security architect has reviewed the changes in this PR,
• [ ] These changes are part of a larger initiative with a separate security review, or
• [ ] There are no security aspects to these changes

[szh]

Is there any way we can include tests for this? It seems like it is a subtle behavior change.