Support access log formatters in EnvoyProxy

[aoledk]

Description:

EG supports access log [^1], no formatters.

Envoy support formatters [^2] when setting access log, such as envoy.formatter.req_without_query [^3], it will remove the query string and is used to avoid logging any sensitive information into the access log. It's very important for production usage.

[optional Relevant Links:] [^1]: https://gateway.envoyproxy.io/latest/api/extension_types/#proxyaccesslogformat [^2]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/core/v3/substitution_format_string.proto#envoy-v3-api-msg-config-core-v3-substitutionformatstring [^3]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/formatter/req_without_query/v3/req_without_query.proto#extension-envoy-formatter-req-without-query

[zirain]

EG should check the format and opt-in formatters.

[aoledk]

@zirain I want to help.