feat: warn users about invalid certificate common name for Cumulocity connections

[reubenmiller]

Proposed changes

Improve the warning for users that have generated the device certificate using external command (e.g. not tedge cert create). In this scenerio the user doesn't get warning during the cert creation, so they are unaware of the problem.

Now the tedge connect c8y will display a warning if an invalid Common Name is detected at connection time, though it will not prevent trying to connect to Cumulocity (in case if this restriction is lifted at some point).

It is only valid for Cumulocity connections as Cumulocity has a defined list of allowed characters in the Common Name.

Below is an example of the warning that is shown to users:

# tedge connect c8y
Connecting to Cumulocity:
        mapper configuration file: /etc/tedge/tedge.toml
        device id: TST_develop_chalky_bullet:invalid
        cloud profile: <none>
        cloud host: example.cumulocity.com:8883
        auth type: Certificate
        certificate file: /etc/tedge/device-certs/tedge-certificate.pem
        cryptoki: off
        bridge: mosquitto
        service manager: systemd
        mosquitto version: 2.0.11
        proxy: Not configured
warning: The device certificate Common Name may not be accepted by the cloud: The string '"TST_develop_chalky_bullet:invalid"' contains characters which cannot be used in a name [use only A-Z, a-z, 0-9, ' = ( ) , - . ? % * _ ! @]
Creating device in Cumulocity cloud... ✗
error: Connection error while creating device in Cumulocity: Mqtt state: Mqtt serialization/deserialization error: IO: received fatal alert: CertificateUnknown: Mqtt serialization/deserialization error: IO: received fatal alert: CertificateUnknown: IO: received fatal alert: CertificateUnknown: received fatal alert: CertificateUnknown

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

#3855

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

[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
860	0	3	860	100	2h39m34.380472s

[codecov]

Codecov Report

❌ Patch coverage is 88.29787% with 11 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/core/tedge/src/cli/connect/command.rs	88.29%	10 Missing and 1 partial ⚠️

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[didier-wenzek]

Approved