Branch alias is not detected by satis

**Describe the bug**
I have a repo in satis, that uses [branch-alias](https://getcomposer.org/doc/articles/aliases.md) and the alias branch-versions are not listed in the satis index.html and package.json - files

**To Reproduce**
- Create a repo that uses [branch-alias] e.g. like this:
```json
"extra": {
"branch-alias": {
"dev-develop": "1.0.x-dev"
}
}
```
- include this repo in your satis-config file
- run `bin\satis.bat build`

**Outcome**
in the index.html it shows
> Releases: dev-master, dev-develop
for this repo.
(json-file for this repo in satis storage shows only config releases "dev-master, dev-develop")

**Expected behavior**
Satis should show / list the branch-alias versions too.

e.g. `composer show` on the included repo shows:
> versions : 1.0.x-dev, * dev-develop

so satis should list version `1.0.x-dev` from the branch-alias in its "releases"-section in index.html and in the json-file for this package.

**Additional context**
I am not sure if this is relevant for this problem, but the included repo is hosted on gitlab.

[branch-alias]: https://getcomposer.org/doc/articles/aliases.md

Start at bin\satis.bat build and trace how the included repository's branch metadata becomes its index.html and package.json entries. Reproduce the branch-alias example with the satis-config, then compare the generated releases with Composer's reported versions; done means 1.0.x-dev appears for the package in both outputs.

Written by the indexing model from the issue text.