Allow extra envoy args to be passed in

[kevinjqiu]

Allow extra envoy CLI option to be passed in. One such use case is when I want to increase/decrease the log level of the envoy sidecar process, I need to run envoy with --log-level xyz or --component-log-level xyz:level

[hashicorp-cla]

All committers have signed the CLA.

[kevinjqiu]

I don't think the test failure is due to my change:

=== Failed
=== FAIL: helper/cert TestGenSource_expiry (600.10s)
=== PAUSE TestGenSource_expiry
=== CONT  TestGenSource_expiry
--- PASS: TestGenSource_expiry (2.20s)
    source_gen_test.go:116: leaf.pem: OK
        
    source_gen_test.go:116: leaf.pem: OK
        
panic: test timed out after 10m0s
...

[lkysow]

Hey Kevin, thanks for the PR. Would this also work as an annotation on the Pod?