Add filewatcher capabilities to kanto-auto-deployer

[vasilvas99]

Problem

We want kanto-auto-deployer to be able to run in two modes:

• one-shot (deploy all manifests in a provided directory and exit)
• daemon (deploy all manifests in a provided directory, keep monitoring it for changes and redeploy any manifests added later/old manifests changed)

Other issues:

• Cargo.toml was not using exact semvers for dependencies, leading to compilation breaking sometimes with rustc 1.59.0
• A more elaborate handling of CLI arguments is required as now we provide more user choice.

Solution

• All dependencies were set to a specific semver and the cargo.lock was regenerated. Now compilations are consistent.
• clap was used as a cli parsing library as it's very flexible and parses the CLI arguments as a strongly typed rust data structure + provides the ability to set default values.

---

A new cli flag --daemon/-d was added that sets the operation mode of KAD.

If the flag is not passed, KAD works in "one-shot" mode (minimal changes here)

If the flag is passed:
The one-shot directory deployment is ran and then an async_watcher is set-up through the new module fs_watch. This module polls the directory every 10 seconds (const POLL_SECONDS: f64 = 10.0;) and if FS events have occurred during that interval it de-bounces them (multiple modifications -> single trigger at the end) it triggers a callback function.

That callback redeploy_on_change goes through all newly added json files/modified existing ones and deploys the containers specified in those manifests. If the container already exists (e.g. it's already deployed) it is first stopped, then removed and created again. This ensures that the latest state described in the manifest will be used when running as a daemon.

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The "filewatcher" feature flag

To reduce binary bloat, all filewatcher/deamon functionality has been "namespaced" under the "filewatcher" compilation flag. This is a default feature, so running cargo build --release will yield a version of KAD that has this mode available for use.

To compile without daemon mode run cargo build --release --no-default-features. This will yield a binary that only has the "one-shot" mode.

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Screenshots:
Help:

One-shot mode:

Daemon mode:

As it can be seen on the screenshots only the created/modified files are taken into account. If the manifest is correct (e.g. vum.json) it will be redeployed. If not (e.g. wrong.json) it would log an error and continue with the monitoring.

Compiled with --no-default-features:

Footprint (on QEMUx86 + kvm) in daemon mode (service):

Size with filewatcher: 4.2 M (most of the increase is due to the clap CLI parser)
RAM usage: 1.4 M
CPU: 0.0 all cores (from htop)

[stlachev]

LGTM