Add beta subdomains

[dskloetd]

Motivation

We want to be able to deploy unreleased versions of the NNS dapp which can be used with the same mainnet principal as the real NNS dapp.

This PR is based on #3255

Changes

1. Add the domains to .well-known/ic-domains so that the boundary node can see that the canister wants to serve on those domains.
2. Add the domains to .well-known/ii-alternative-origins so the internet identity known those domains are allowed to use the same derivation origin.
3. Add the domains to NNS_IC_ORG_ALTERNATIVE_ORIGINS so that nns-dapp knows to request the canonical derivation origin from internet identity when serving from those domains.

Tests

1. Unit tests added.
2. Downloaded https://qsgjb-riaaa-aaaaa-aaaga-cai.dskloet-ingress.devenv.dfinity.network/.well-known/ic-domains and got

nns.internetcomputer.org
wallet.internetcomputer.org
wallet.ic0.app
beta.nns.internetcomputer.org
beta.nns.ic0.app

3. Downloaded https://qsgjb-riaaa-aaaaa-aaaga-cai.dskloet-ingress.devenv.dfinity.network/.well-known/ii-alternative-origins and got

{"alternativeOrigins": ["https://nns.internetcomputer.org", "https://wallet.internetcomputer.org", "https://wallet.ic0.app", "https://beta.nns.internetcomputer.org", "https://beta.nns.ic0.app"]}

Todos

• Add entry to changelog (if necessary).

[mstrasinskis]

LGTM, thanks!