Add support for custom package hosts

[julien-neon]

Is your feature request related to a problem? Please describe.

I wrote a custom lint package with custom_lint_builder and published it to my private pub repo. When including my custom lint package locally, the lints show up as expected, but when I referenced the published version of my lint package:

my_lints:
    hosted: https://onepub.dev/api/my-repo-id/
    version: ^1.0.0+1

the lints did not show up anymore. When running flutter pub run custom_lint, I get the following error:

The request analysis.setContextRoots failed with the following error:
RequestErrorCode.PLUGIN_ERROR
Exception: Failed to run "pub get" in the client project:
Resolving dependencies...

Because custom_lint_client depends on my_lints any which doesn't exist (could not find package my_lints at https://pub.dev), version solving failed.

at:
#0      CustomLintWorkspace.runPubGet (package:custom_lint/src/workspace.dart:760:7)
<asynchronous suspension>
#1      CustomLintWorkspace.resolvePluginHost (package:custom_lint/src/workspace.dart:744:5)
<asynchronous suspension>
#2      SocketCustomLintServerToClientChannel._startProcess (package:custom_lint/src/v2/server_to_client_channel.dart:151:7)
<asynchronous suspension>
#3      SocketCustomLintServerToClientChannel.init (package:custom_lint/src/v2/server_to_client_channel.dart:111:21)
<asynchronous suspension>
#4      CustomLintServer._maybeSpawnCustomLintPlugin (package:custom_lint/src/v2/custom_lint_analyzer_plugin.dart:394:5)
<asynchronous suspension>
#5      CustomLintServer._handleAnalysisSetContextRoots.<anonymous closure> (package:custom_lint/src/v2/custom_lint_analyzer_plugin.dart:341:9)
<asynchronous suspension>
#6      PendingOperation.run (package:custom_lint/src/async_operation.dart:22:14)
<asynchronous suspension>
#7      CustomLintServer._handleRequest (package:custom_lint/src/v2/custom_lint_analyzer_plugin.dart:173:22)
<asynchronous suspension>

_PrettyRequestFailure: {"code":"PLUGIN_ERROR","message":"Exception: Failed to run \"pub get\" in the client project:\nResolving dependencies...\n\nBecause custom_lint_client depends on my_lints any which doesn't exist (could not find package my_lints at https://pub.dev), version solving failed.\n","stackTrace":"#0      CustomLintWorkspace.runPubGet (package:custom_lint/src/workspace.dart:760:7)\n<asynchronous suspension>\n#1      CustomLintWorkspace.resolvePluginHost (package:custom_lint/src/workspace.dart:744:5)\n<asynchronous suspension>\n#2      SocketCustomLintServerToClientChannel._startProcess (package:custom_lint/src/v2/server_to_client_channel.dart:151:7)\n<asynchronous suspension>\n#3      SocketCustomLintServerToClientChannel.init (package:custom_lint/src/v2/server_to_client_channel.dart:111:21)\n<asynchronous suspension>\n#4      CustomLintServer._maybeSpawnCustomLintPlugin (package:custom_lint/src/v2/custom_lint_analyzer_plugin.dart:394:5)\n<asynchronous suspension>\n#5      CustomLintServer._handleAnalysisSetContextRoots.<anonymous closure> (package:custom_lint/src/v2/custom_lint_analyzer_plugin.dart:341:9)\n<asynchronous suspension>\n#6      PendingOperation.run (package:custom_lint/src/async_operation.dart:22:14)\n<asynchronous suspension>\n#7      CustomLintServer._handleRequest (package:custom_lint/src/v2/custom_lint_analyzer_plugin.dart:173:22)\n<asynchronous suspension>\n"}
#0      ChannelBase.sendRequest (package:custom_lint/src/server_isolate_channel.dart:82:7)
<asynchronous suspension>
#1      CustomLintRunner.initialize.<anonymous closure> (package:custom_lint/src/runner.dart:43:5)
<asynchronous suspension>
#2      _runServer.<anonymous closure> (package:custom_lint/custom_lint.dart:96:7)
<asynchronous suspension>
#3      _AsyncCompleter.complete (dart:async/future_impl.dart:41:3)
<asynchronous suspension>
#4      _runServer.<anonymous closure> (package:custom_lint/custom_lint.dart:126:19)
<asynchronous suspension>
#5      _runServer (package:custom_lint/custom_lint.dart:86:3)
<asynchronous suspension>
#6      customLint (package:custom_lint/custom_lint.dart:50:5)
<asynchronous suspension>
#7      entrypoint (file:///Users/julien/.pub-cache/hosted/pub.dev/custom_lint-0.6.8/bin/custom_lint.dart:68:3)
<asynchronous suspension>
#8      main (file:///Users/julien/.pub-cache/hosted/pub.dev/custom_lint-0.6.8/bin/custom_lint.dart:80:5)
<asynchronous suspension>

A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

Describe the solution you'd like

I would like the possibility to include private packages when running custom lints. I am currently using OnePub for my private pub repo and its CLI has me logged in all the time. So when I run flutter pub get in the command-line it works out of the box. Judging from the current implementation of custom_lint/src/workspace.dart the two options are: resolving package host locally and from pub.dev. Am I missing something? Otherwise I would request the support for custom hosts.

Describe alternatives you've considered
I cannot publish the linter package, as it is considered company property. Not sure if I am missing something.

Additional context
Add any other context or screenshots about the feature request here.