feat: sm-plugin for flows

[rina23q]

Proposed changes

This pull request introduces the new tedge-flows-plugin package and a binary symlinked to /etc/tedge/sm-plugin/flow.

The plugin supports only 3 commands:

1. list
2. install
3. remove

Note: update-list is unsupported, therefore, it returns 1 as in the sm-plugin specification.

Naming rules

Look at #4037 (comment).

Installation rules

• No hard check for the given --module-version <version>. If given, it will be used to check the provided version equals to the one installed.
• Installing a flow onto the top level is unsupported whilst nested layers are possible; simply, because it's impossible to distinguish if user wants it at the top level or second level, from the naming rule local/toplevel and local/second.
• Attempts to unpack if a provided file path doesn't have .tar or .tar.gz. At first, I didn't implement this fallback, however, I found that the file extension is missing while downloading a file... If there was no fallback, integration with c8y won't work :/

Removal rules

• ignores --module-version <version>.
• params.toml will be kept only if flows.params.keep_on_delete is true (default: false).

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

#3986

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

[codecov]

Codecov Report

❌ Patch coverage is 80.21828% with 145 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
plugins/tedge_flows_plugin/src/lib.rs	45.37%	63 Missing and 2 partials ⚠️
plugins/tedge_flows_plugin/src/install.rs	80.50%	38 Missing and 8 partials ⚠️
plugins/tedge_flows_plugin/src/list.rs	93.90%	14 Missing and 1 partial ⚠️
plugins/tedge_flows_plugin/src/remove.rs	93.33%	2 Missing and 6 partials ⚠️
plugins/tedge_flows_plugin/src/error.rs	0.00%	6 Missing ⚠️
crates/core/tedge/src/main.rs	16.66%	0 Missing and 5 partials ⚠️

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[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
879	0	3	879	100	2h50m37.039040999s

[rina23q]

The system test Install fails with an invalid flow requires a change on the exit code of tedge flows list.
=> Solved by #4060. Now rebased to apply the upstream change.

[didier-wenzek]

Approved. A great addition that will support users writing, sharing and deploying domain specific flows. Thank you.

[Bravo555]

All the feedback addressed, with a very comprehensive set of tests.

[Bravo555]

thought: A bit annoying that we have to spawn a process instead of directly using the same function that tedge flows list does, but there shouldn't be a problem either way.

[reubenmiller]

Calling the binary is ok, though we need to make sure we pass the loaded config_dir (that the agent is using), and pass it to the tedge flows list command, e.g.

tedge flows list --flows-dir "foo" --config-dir /tmp/tedge

[rina23q]

Commited here: 8be1996

[reubenmiller]

Approved. Really nice addition. Thanks for updating the log messages to be more verbose as this will be extremely helpful when reading the operation logs for installing and removing flows from the cloud