Anchor links to individual pilot env vars

[nrfox]

There's a lot of features that are controlled through setting environment variables in pilot. There is an anchor link to the table with all the env vars but the table is large and it would be nice to be able to link and jump to a specific env var in the table. For example: a link like https://istio.io/latest/docs/reference/commands/pilot-discovery/#envvars-enable-native-sidecars to jump to the ENABLE_NATIVE_SIDECARS env var in the table.