Istio 1.8 support

[Sodman]

Description

Adds support for deploying wasm filters to Istio 1.8.x.

Context

The release of Istio 1.8.x is coming up, so we want to make sure users can deploy to it right away once it's out.

This PR adds support to wasme to deploy wasm filters to Istio 1.8.x.

The ABI used by Istio 1.7.x is compatible with Istio 1.8.x so any filters built for Istio 1.7.x should work in 1.8.x.

Notes:

• Tested against Istio release istio-1.8.0-alpha.0
• Tested CPP filter webassemblyhub.io/sodman/istio-1-7:v0.3
• Tested Rust filter webassemblyhub.io/sodman/rust-example:v0.2
• Tested Assemblyscript with webassemblyhub.io/sodman/as-istio-1-7:v0.3
• Tested Tinygo with webassemblyhub.io/sodman/tinygo-example:v0.1

Checklist:

• I included a concise, user-facing changelog (for details, see https://github.com/solo-io/go-utils/tree/master/changelogutils) which references the issue that is resolved.
• If I updated APIs (our protos) or helm values, I ran make install-deps generated-code from tools/wasme/cli to ensure there will be no code diff
• I followed guidelines laid out in the Gloo contribution guide
• I opened a draft PR or added the work in progress label if my PR is not ready for review
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works