Enable fingerprint xsd validation and CI automation

[dabdine]

Description

• Enables XML validation in recog_verify via XSD for fingerprint files using the already-existing fingerprints.xsd schema.
• Configures the XML extension in vscode to properly autocomplete and validate recog XML files if the extension is installed.
• Updates the background monitor to automatically validate via XSD as well

This does not change any behavior (yet) in Go or Java, however.

Motivation and Context

Malformed XML is not handled well by recog_verify. In most cases, when a malformed document is produced, recog_verify will simply dump a stack trace. This change will now properly report validation errors as errors in the same format as example errors that were previously produced.

This should allow new PR submissions to pass more strict testing automatically, keeping the quality bar high while avoiding the burden on the reviewer for checking whether certain attributes & elements are present, and set to the right values.

How Has This Been Tested?

bundle exec rake tests

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• [x] I have updated the documentation accordingly (or changes are not required).
• [x] I have added tests to cover my changes (or new tests are not required).
• [x] All new and existing tests passed.

[dabdine]

Here's an example of an XML change (_encoding="base65") which will break CI because base65 is not in the enumeration allowed for the _encoding attribute, as specified by fingerprints.xsd:

https://github.com/dabdine/recog/pull/1

You'll see this in the log:

xml/telnet_banners.xml:67: FAIL: 67:0: ERROR: Element 'example', attribute '_encoding': [facet 'enumeration'] The value 'base65' is not an element of the set {'base64'}.