Add support for HTTP proxying (#506)

* Add `--proxy` and `--no-proxy` CLI flags
* Add property `http` to `pkl:settings`
* Move `EvaluatorSettings` from `pkl:Project` to its own module and add property `http`
* Add support for proxying in server mode, and through Gradle
* Add `setProxy()` to `HttpClient`
* Add documentation

pkl-executor/gradle.lockfile

@@ -2,10 +2,10 @@
 # Manual edits can break the build and are not advised.
 # This file is expected to be part of source control.
 com.tunnelvisionlabs:antlr4-runtime:4.9.0=testRuntimeClasspath
-net.bytebuddy:byte-buddy:1.14.11=testCompileClasspath,testImplementationDependenciesMetadata,testRuntimeClasspath
+net.bytebuddy:byte-buddy:1.14.16=testCompileClasspath,testImplementationDependenciesMetadata,testRuntimeClasspath
 net.java.dev.jna:jna:5.6.0=kotlinCompilerClasspath,kotlinKlibCommonizerClasspath
 org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath,testImplementationDependenciesMetadata,testRuntimeOnlyDependenciesMetadata
-org.assertj:assertj-core:3.25.3=testCompileClasspath,testImplementationDependenciesMetadata,testRuntimeClasspath
+org.assertj:assertj-core:3.26.0=testCompileClasspath,testImplementationDependenciesMetadata,testRuntimeClasspath
 org.graalvm.sdk:graal-sdk:23.0.2=testRuntimeClasspath
 org.graalvm.truffle:truffle-api:23.0.2=testRuntimeClasspath
 org.jetbrains.intellij.deps:trove4j:1.0.20200330=kotlinCompilerClasspath,kotlinKlibCommonizerClasspath

pkl-executor/src/test/kotlin/org/pkl/executor/EmbeddedExecutorTest.kt

@@ -41,7 +41,7 @@ class EmbeddedExecutorTest {
     }
     override fun toString(): String = name
   }
-  
+
   companion object {
     @JvmStatic
     private val allTestExecutors: List<TestExecutor> by lazy {