Improve links in the documentation

[Tschakki]

Is your feature request related to a problem? Please describe. Sometimes link labels are confusing and they are not indicating where exactly the link is leading .

Describe the solution you'd like

A standard for link labels should be developed, that helps indicating where the link is taking the user.

There should be link label guidelines for:

• external links, indicating it is external, and to which page it is going, e.g. GitHub.
• links to other docs-components
• links to other pages
• links on the same page

These guidelines then need to be applied in all latest documentations.

• [ ] Create guidelines for links in the documentation
• [ ] Apply for latest Lisk SDK docs
• [ ] Apply for latest Lisk Service docs
• [ ] Apply for latest Lisk Core docs

[Tschakki]

See: https://developers.google.com/style/link-text