tedge cert renew uses the existing key to create a new certificate

[rina23q]

Proposed changes

This PR changes the behaviour of tedge cert renew. The work on #2502 defines that renew = remove + create, however, as #2512 is created, renew should reuse the private key and create only a new certificate.

At first, I thought I should have changed the robot tests regarding tedge cert renew, but I changed my mind. Indeed, the tests pass and they test the validity of the new certificate. So, I decided not to change them.

tests/RobotFramework/tests/tedge/tedge_upload_cert.robot

• Renew the certificate
• Renew certificate fails

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

#2512

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s)
• I ran cargo fmt as mentioned in CODING_GUIDELINES
• I used cargo clippy 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

[codecov]

Codecov Report

Merging #2520 (21166d8) into main (290c50c) will increase coverage by 0.2%.
Report is 3 commits behind head on main.
The diff coverage is 94.3%.

❗ Current head 21166d8 differs from pull request most recent head 3052f95. Consider uploading reports for the commit 3052f95 to get more accurate results

Additional details and impacted files

Files	Coverage Δ
crates/common/certificate/src/lib.rs	87.5% <95.2%> (+<0.1%)	⬆️
crates/core/tedge/src/cli/certificate/renew.rs	76.6% <97.3%> (+15.7%)	⬆️
crates/core/tedge/src/cli/certificate/create.rs	88.5% <90.0%> (+1.8%)	⬆️

... and 10 files with indirect coverage changes

[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
370	0	3	370	100	55m46.632999999s

[didier-wenzek]

This is in a good shape.

[didier-wenzek]

Approved