HNC: Add excluded namespace configuration to v0.8 release note and installation note.

[yiqigao217]

Update the installation note with setting excluded namespaces in v0.8 release note and here.

[yiqigao217]

In addition, since we migrated to v1 APIs for CRD, VWH, MWH #1434, we need to add that

• HNC v0.8 requires K8s 1.16+ since only v1.16+ can create v1 webhooks.

[yiqigao217]

Just adding another scenario to the doc: what if to exclude a namespace already with subns anchors - see detailed instruction at #1483 (comment).

[adrianludwin]

Hmm, just realized I didn't address the comment for #1483. I'll file a bug to the docs that say "don't do this" :)