Add support for self config source

[jrhee17]

Motivation:

This pull request adds support for SELF config source types. This feature allows the control plane to delegate the decision of which protocol to use to the client.
Reference: https://github.com/envoyproxy/envoy/blob/bd18d0fa7790a7e5fe1a95f6ae271ca02614e36c/api/envoy/config/core/v3/config_source.proto#L239

Note that this implementation may not have been completed from envoy side, so we should use this option with caution.
ref: envoyproxy/envoy#13951

Modifications:

• The dependency relationship between ResourceNode and ConfigSource has changed. This can be a problem because the configSource specified in ResourceNode#ConfigSource can be different from the actual ConfigSource used for subscribing. Modified so that ConfigSource is computed before creating a ResourceNode.
• Renamed BootstrapApiConfigs to ConfigSourceMapper since it better represents the functionality of the class.
• Added parentConfigSource to the logic of computing a new configSource.
• Modified so that subscribed ResourceNode#configSource is always non-null. The only case where this is null is for static clusters (bootstrap clusters)

Result:

• SELF type configSource is now supported

[github-actions]

🔍 Build Scan® (commit: 5c7c076)

Job name	Status	Build Scan®
build-windows-latest-jdk-19	✅	https://ge.armeria.dev/s/nr5wajdfyhr3g
build-self-hosted-unsafe-jdk-8	✅	https://ge.armeria.dev/s/avoh4hayvffse
build-self-hosted-unsafe-jdk-19-snapshot-blockhound	✅	https://ge.armeria.dev/s/qegj7venqyrc4
build-self-hosted-unsafe-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/jiu7c3ssdfiju
build-self-hosted-unsafe-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/kodynqf53zbiq
build-self-hosted-unsafe-jdk-17-leak	✅	https://ge.armeria.dev/s/edo7eqdyhpzds
build-self-hosted-unsafe-jdk-11	✅	https://ge.armeria.dev/s/oxr5qbxm6z4ik
build-macos-12-jdk-19	✅	https://ge.armeria.dev/s/puxr42xbrhsoe

[minwoox]

Modified so that subscribed ResourceNode#configSource is always non-null.

Let's remove Nullable in the ListenerResourceNode constructor.

[jrhee17]

Let's remove Nullable in the ListenerResourceNode constructor.

Coincidentally, due to the recent changes now ListenerRoot can pass a null config source

armeria/xds/src/main/java/com/linecorp/armeria/xds/ListenerRoot.java

Line 37 in 42edbb2

node = new ListenerResourceNode(null, resourceName, xdsBootstrap, this, ResourceNodeType.STATIC);

[minwoox]

Looks very useful. Thanks! 👍 👍 👍

[codecov]

Codecov Report

Attention: Patch coverage is 62.50000% with 21 lines in your changes are missing coverage. Please review.

Project coverage is 74.10%. Comparing base (42edbb2) to head (5c7c076).
Report is 7 commits behind head on main.

Files	Patch %	Lines
...a/com/linecorp/armeria/xds/ConfigSourceMapper.java	40.62%	13 Missing and 6 partials ⚠️
...ava/com/linecorp/armeria/xds/XdsBootstrapImpl.java	88.88%	0 Missing and 1 partial ⚠️
...ava/com/linecorp/armeria/xds/XdsConverterUtil.java	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #5459   +/-   ##
=========================================
  Coverage     74.09%   74.10%           
- Complexity    20968    20993   +25     
=========================================
  Files          1817     1818    +1     
  Lines         77187    77273   +86     
  Branches       9854     9867   +13     
=========================================
+ Hits          57194    57262   +68     
- Misses        15323    15326    +3     
- Partials       4670     4685   +15     

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[ikhoon]

�Though it is not a standard feature, it could be useful. 🙇‍♂️🙇‍♂️

[ikhoon]

Still LGTM.