fix(cli): add logic to handle a case where CI is setting an env variable

What?

Scope of the PR:

Adding a new check to resolve an issue in case a an env variable is set inside GitHub action like this:
name: Deploy env: STORYBLOK_PERSONAL_ACCESS_TOKEN: ${{secrets.STORYBLOK_PERSONAL_ACCESS_TOKEN}} run: yarn workspace commerce-layer deploy --skipPrompts



- _Refactoring_ `getPersonalAccessToken()` function to make it more clear and readable.

TODO: 
- [ ] Adding this new way of call deploy command inside the README.md

## Why?
You can find a more detailed description inside JIRA: [EXT-2013](https://storyblok.atlassian.net/browse/EXT-2013)

[EXT-2013]: https://storyblok.atlassian.net/browse/EXT-2013?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

storyblok / field-plugin

fix(cli): add logic to handle a case where CI is setting an env variable #279

What?