add a snyk policy file (opendatahub-io#241)

We want the Snyk run to skip verification of the `benchmarks`,
`examples` and `tests` directories because Snyk will report a variety of
issues that are not relevant to the repository's code.

An additional set of individual vulnerabilities in the rest of the
source code are ignored at the Snyk server level, with reasons
specified.

The Snyk security scan on this PR shows that there are only a few
individual issues remaining to be addressed. These are flagged in
[INFERENG-985: Review issues of concern raised by Snyk security
scan](https://issues.redhat.com/browse/INFERENG-985) for follow up.

Author: derekk-nm

.snyk

@@ -0,0 +1,7 @@
+# Snyk (https://snyk.io) policy file, patches or ignores known vulnerabilities
+version: v1.25.0
+exclude:
+ global:
+   - examples/
+   - tests/
+   - benchmarks/