Added Vigil

[Ki-er]

With the merge of #3186, this will close #3166
Source Code: https://github.com/valeriansaliou/vigil
Installation: https://github.com/valeriansaliou/vigil#installation

Install from source:
The last option is to pull the source code from Git and compile Vigil via cargo:
cargo build --release
You can find the built binaries in the ./target/release directory.
Install libssl-dev (ie. OpenSSL headers) and libstrophe-dev (ie. XMPP library headers; only if you need the XMPP notifier) before you compile Vigil. SSL dependencies are required for the HTTPS probes and email notifications.

Install from Docker Hub:
You might find it convenient to run Vigil via Docker. You can find the pre-built Vigil image on Docker Hub as valeriansaliou/vigil.

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[Ki-er]

Closing due to #3269

[nodiscc]

Made obsolete by #3269