Support recovery after translation errors

*Description*:
Currently, EG may work in either `FailOpen` or `FailClosed` mode when encountering XDS translation errors. Errors can stem from invalid resources or transient failures (e.g. in connection to the extension server).

When failures occur, a best-effort XDS state is stored, which is likely disruptive to end users, either due to wiped-out routes and listeners or due to partially translated configuration.

EG should attempt to recover from failed translations. This can be accomplished by:
- Retrying translation (with delay and backoff)
- Retriggering translation when errors are fixed: malformed resources are fixed by users (already supported), connectivity to extension server is restored.
- Periodically reconciling XDS to fix entropy

Ideally, the message framework in EG should be used to trigger a recovery/retry translation. Components such as Extension Manager and XDS Translator should be able to trigger a retry/recover translation by publishing a relevant message.

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