Add Support for Dockerfile.<some-env>

[MattMorgis]

I think this closes #102 and #192

It should add icon and syntax support for Dockerfile.<some-env>

Before:

After:

[chrisdias]

@MattMorgis thanks for the PR. We've gone back and forth on the glob pattern here (see #193 (comment) for example). There's a workaround to use files.associations in settings:

    "files.associations": {
        "Dockerfile-centos": "dockerfile"
    }

Another idea was to have a setting that let you customize the glob pattern for your environment that people seemed to like (#102 (comment)). I'd be more inclined to take a PR for that than switching up the glob pattern again.

[StephenWeatherford]

@chrisdias, @fiveisprime I don't see the drawback of adding * to the default dockerfile glob pattern, whether or not we add customization of it. I'd like to get this merged (with minor changes). Do you disagree? The compose file glob already has that:

export const FROM_DIRECTIVE_PATTERN = /^\sFROM\s([\w-/:])(\sAS\s*[a-z][a-z0-9-_\.])?$/i;
export const COMPOSE_FILE_GLOB_PATTERN = '**/[dD]ocker-[cC]ompose.{yaml,yml}';
export const DOCKERFILE_GLOB_PATTERN = '**/{*.dockerfile,[dD]ocker[fF]ile}';

[chrisdias]

The pattern used to be more permissive, but then it was too intrusive. See #134 for the original issue where we changed it to what it is today. I like the idea of making this a setting so that it can be controlled by the user.

[MattMorgis]

I like the idea of making this a setting, too. I will poke around and update this PR.

[ejizba]

FYI this PR was created before our recent switch from Travis CI to Azure Dev Ops. Push a commit (merging with master or addressing comments) and the "checks" for this PR will be updated

[ejizba]

Closing this PR since this solution is too intrusive as mentioned above and hasn't had any recent activity. We're actively investigating the alternative approach to add settings for these glob patterns