rumqttc: TLS Key encoding fix

[ijager]

Type of change

Breaking Change

Checklist:

• Formatted with cargo fmt
• Make an entry to CHANGELOG.md if it's relevant to the users of the library. If it's not relevant mention why.

Description

This PR lets users of rumqttc use any of the Rustls supported key encodings [RSA (PKCS#1), PKCS#8, SEC1].

This issue addresses #751

I left the Key enum as is to prevent a breaking change, however it does no longer matter if the user choses RSA or ECC. For a cleaner API I think the Key enum could be removed.

[ijager]

• Commit 1 implemented this by adding a new variant.
• Commit 2 uses rustls_pemfile::read_one to avoid breaking changes.

[ijager]

Tested with

• RSA (PKCS#1) key for RSA
• PKCS#8 key for RSA
• SEC1 key for ECDSA

[ijager]

As discussed in #751 I have removed the Key enum. This is documented in the changelog. Examples are also updated.

[swanandx]

Thank you for the PR! Looks like Key is still there in lib.rs ( that is why CI is failing ), please fix it as well : )

PS: This is a breaking change, so can we please update the PR description to clarify it?

[ijager]

Not sure why that test failed, seems unrelated?

[swanandx]

Not sure why that test failed, seems unrelated?

Yup, it keeps failing randomly 😜

[swanandx]

Thank you for the PR!