Proposed changes

Improve the compatibility of the tedge with other tooling which can be used for creating Certificate Signing Requests (CSRs). For example, the gnutls certtool (which supports creating CSRs from private keys stored in HSMs via PKCS11)
processes CSR files which use an older BEGIN/END blocks, and can also contain additional details about the CSR in plain text (so it is readable for humans).

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

#3546

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s. You can activate automatic signing by running just prepare-dev once)
• I ran just format as mentioned in CODING_GUIDELINES
• I used just check as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments