Introduce the notion of a default SessionProtocol

[jrhee17]

Motivation:

It has been suggested that SessionProtocol.UNDEFINED be avoided at #6060 (comment), and a default SessionProtocol for clients is introduced.

A client can now be created without the user explicitly providing a SessionProtocol. By default SessionProtocol.HTTP will be used. For clients that are created with a String, users will be able to use the default SessionProtocol via scheme relative URIs as defined in the following rfc.

WebClient.builder("//armeria.dev").build()
WebClient.builder(new URI(null, "armeria.dev", null, null)).build()
WebClient.builder(Endpoint.of("armeria.dev")
WebClient.builder(Endpoint.of("armeria.dev"), "/").build()
WebClient.of().blocking().get("//armeria.dev/hello")

One point to note is that RequestTarget may be parsed different depending on whether the input is a path, or a uri.
In the context of a path, //my-path is a completely valid path whereas in the context of a URI, //my-path will be a uri with authority my-path.
In order to address this, DefaultRequestTarget#forClientPath has been introduced.

Possibly breaking behavior is that requests cannot be made using a path starting with //.

Modifications:

• Added factory methods to use the default SessionProtocol as defined by SessionProtocolUtil#defaultSessionProtocol.
• Added scheme-relative URI handling logic when parsing the authority in RequestTarget#forClient
• Added RequestTarget#forClientPath and modified existing callers to use the new API when applicable

Result:

• Users may create a client without explicitly specifying the SessionProtocol

[github-actions]

🔍 Build Scan® (commit: f9cb6bd)

Job name	Status	Build Scan®
build-ubicloud-standard-16-jdk-8	✅	https://ge.armeria.dev/s/7ltmmq2ho5sgs
build-ubicloud-standard-16-jdk-21-snapshot-blockhound	✅	https://ge.armeria.dev/s/hsjudmfrlu2tc
build-ubicloud-standard-16-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/7wnw4zqia2elm
build-ubicloud-standard-16-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/yuqbtdrqu4z62
build-ubicloud-standard-16-jdk-17-leak	✅	https://ge.armeria.dev/s/opsbq6s4qtat2
build-ubicloud-standard-16-jdk-11	✅	https://ge.armeria.dev/s/awgyqwymhiqha
build-macos-latest-jdk-21	✅	https://ge.armeria.dev/s/37rbo6aoxrssq

[codecov]

Codecov Report

Attention: Patch coverage is 84.09091% with 14 lines in your changes missing coverage. Please review.

Project coverage is 74.40%. Comparing base (3b27340) to head (f9cb6bd).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
...rp/armeria/internal/common/RequestTargetCache.java	66.66%	0 Missing and 3 partials ⚠️
.../linecorp/armeria/client/thrift/ThriftClients.java	57.14%	3 Missing ⚠️
...p/armeria/internal/client/SessionProtocolUtil.java	71.42%	2 Missing ⚠️
...orp/armeria/client/eureka/EurekaEndpointGroup.java	0.00%	2 Missing ⚠️
.../armeria/server/eureka/EurekaUpdatingListener.java	0.00%	2 Missing ⚠️
.../com/linecorp/armeria/client/grpc/GrpcClients.java	50.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6128      +/-   ##
============================================
- Coverage     74.44%   74.40%   -0.04%     
- Complexity    22059    22219     +160     
============================================
  Files          1942     1960      +18     
  Lines         82033    82333     +300     
  Branches      10736    10740       +4     
============================================
+ Hits          61070    61262     +192     
- Misses        15854    15948      +94     
- Partials       5109     5123      +14     

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