Introduce XdsCentralDogmaBuilder

[jrhee17]

Motivation

CentralDogma is used deployed in multiple regions/zones. Given that we will soon be supporting zone-aware load balancing from Armeria's side, we can use CentralDogma to take advantage of zone-aware load balancing.

For instance:

• we may route only reads to the CentralDogma in the same zone, whereas write requests will be done to a single pre-designated zone.
• in DR situations, we can quickly route traffic between zones dynamically

Modifications

• Introduced XdsCentralDogmaBuilder, which builds an ArmeriaCentralDogma based on parameters
  • Most methods in AbstractArmeriaCentralDogmaBuilder didn't make sense for xDS, so AbstractCentralDogmaBuilder is extended directly
• Moved ArmeriaCentralDogma from the client package to the internal package so that XdsCentralDogmaBuilder can also build an ArmeriaCentralDogma.
• The CentralDogma created by XdsCentralDogmaBuilder creates an XdsBootstrap internally that should be closed. For this reason, CentralDogma now inherits AutoCloseable which closes underlying resources such as XdsBootstrap or EndpointGroup.
• Misc) Modified CentralDogmaRuleDelegate since configuring a CentralDogmaExtension with server#port threw an exception since the ipv6 scope id wasn't understood.

Result

• java-armeria-xds client is introduced

[ikhoon]

Looks good! 👍👍

[minwoox]

Looks awesome. 👍 👍 👍