feat: support default path environment variable

[liweitian]

Description

Allow user to set default path as an environment variable. If the path is invalid, we still set it to path.join(os.homedir(), 'Documents', 'Composer').

Did a merge operation on data.json and data.template.json if it already exists.

Task Item

Closes #1610
Closes #1363

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have functionally tested my change

Screenshots

Please include screenshots or gifs if your PR include UX changes.

[github-actions]

Coverage increased (+0.08%) to 39.918% when pulling 96b8348 on liweitian/updateDefaultFolder into 9e70664 on master.

[liweitian]

@a-b-r-o-w-n I changed the condition in the migration. The previous one would only check whether the data.json contain the defaultPath. But we still need to set it if the defaultPath changed by user.

And I added the following code.
let folder = process.env.COMPOSER_BOTS_FOLDER;
if (folder && folder.endsWith(':')) {
folder = folder + '/';
}

The issue is quite odd here: if user set the defaultPath as D: we use fs.existsSync('D:') in many places to check whether the path is valid, and it will return true. However, Path.resolve('D:') will return the current folder D:\BotFramework-Composer\Composer\packages\server>, which means for path module D: is invalid. I feel the fs and path module are not designed consistent. I searched online but cannot find an elegant way to solve this. I checked our code in the FileSelector.tsx we have itemPath = itemPath[itemPath.length - 1] === ':' ? ${itemPath}/ : itemPath;

it can be reproduced by setting the COMPOSER_BOTS_FOLDER D: and do the migration. Go to localhost:3000, click New, Click next. The location there is not D: but D:\BotFramework-Composer\Composer\packages\server>