fix: apply delay to mqtt connect errors by default

[Bravo555]

Proposed changes

Instead of retrying MQTT connection immediately for some errors, apply delay before retrying connection by default for all errors.

One could argue that for errors where we know we're going to receive it again, e.g. misconfiguring certificates, we should exit instead of retrying, but because rumqttc doesn't organize its errors very well, it would be hard to ensure that every variant is covered, whereas this is simple and works.

Types of changes

• [x] 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

• https://github.com/thin-edge/thin-edge.io/issues/2728

Checklist

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

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 76.6%. Comparing base (e7bf843) to head (c0b0f6a). Report is 1 commits behind head on main.

Additional details and impacted files

| [Files](https://app.codecov.io/gh/thin-edge/thin-edge.io/pull/2832?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=thin-edge) | Coverage Δ | | |---|---|---| | [crates/common/mqtt\_channel/src/connection.rs](https://app.codecov.io/gh/thin-edge/thin-edge.io/pull/2832?src=pr&el=tree&filepath=crates%2Fcommon%2Fmqtt_channel%2Fsrc%2Fconnection.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=thin-edge#diff-Y3JhdGVzL2NvbW1vbi9tcXR0X2NoYW5uZWwvc3JjL2Nvbm5lY3Rpb24ucnM=) | `60.0% <0.0%> (+4.4%)` | :arrow_up: | ... and [3 files with indirect coverage changes](https://app.codecov.io/gh/thin-edge/thin-edge.io/pull/2832/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=thin-edge)

[github-actions[bot]]

Robot Results

:white_check_mark: Passed	:x: Failed	:next_track_button: Skipped	Total	Pass %	:stopwatch: Duration
429	0	3	429	100	0s