smithy4sUpdateLSPConfig: support credentials

[kubukoz]

Some repositories may need credentials (which can be configured with "httpCredentials": "user:pass"), so if we generate their config, it would be valuable to write creds too.

I think this should require an explicit opt-in, such as a setting like smithy4sLSPConfigCredentials := true.

Alternatively, we should detect already-existing repositories with credentials, and not add duplicate entries for them (right now, I see such entries being added).

To reproduce:

project/plugins.sbt:

addSbtPlugin(
  "com.disneystreaming.smithy4s" % "smithy4s-sbt-codegen" % "0.18.23"
)

build.sbt:

val root = project
  .in(file("."))
  .enablePlugins(Smithy4sCodegenPlugin)
  .settings(
    resolvers ++= Resolver.sonatypeOssRepos("snapshots")
  )

smithy-build.json:

{
  "version": "1.0",
  "sources": ["src/main/smithy", "target/scala-2.12/src_managed/main/smithy"],
  "maven": {
    "dependencies": [
      "com.disneystreaming.alloy:alloy-core:0.3.8",
      "com.disneystreaming.smithy4s:smithy4s-protocol:0.18.23",
      "com.disneystreaming.alloy:alloy-core:0.3.9"
    ],
    "repositories": [
      {
        "url": "https://oss.sonatype.org/content/repositories/snapshots",
        "httpCredentials": "myusername:mypass"
      },
      {
        "url": "https://s01.oss.sonatype.org/content/repositories/snapshots"
      }
    ]
  }
}

Run sbt smithy4sUpdateLSPConfig, your smithy-build changes to (formatted):

{
  "version": "1.0",
  "sources": ["src/main/smithy", "target/scala-2.12/src_managed/main/smithy"],
  "maven": {
    "dependencies": [
      "com.disneystreaming.alloy:alloy-core:0.3.8",
      "com.disneystreaming.smithy4s:smithy4s-protocol:0.18.23",
      "com.disneystreaming.alloy:alloy-core:0.3.9"
    ],
    "repositories": [
      {
        "url": "https://oss.sonatype.org/content/repositories/snapshots",
        "httpCredentials": "myusername:mypass"
      },
      {
        "url": "https://s01.oss.sonatype.org/content/repositories/snapshots"
      },
      {
        "url": "https://oss.sonatype.org/content/repositories/snapshots"
      }
    ]
  }
}

i.e. the last entry is added, duplicating / conflicting with the first one.