feat: add Client::certificate_parts() method

[jrconlin]

Description

This was a method that was missed during the initial PR merge. It allows the Client to be built using an imported set of PEM components.

How Has This Been Tested?

A unit test has been added with test cert / key values

Due Dilligence

• [ ] Breaking change
• [ ] Requires a documentation update
• [ ] Requires a e2e/integration test update

[jrconlin]

No worries, and no rush!

Thank you, again, for taking on this library. Hopefully, that should be the last of the post merge updates.

[HarryET]

v0.7.1 has just been published with these changes