Review [license] section in modules

**Jetty version(s)**
9.4+

**Description**
`[license]` sections of Jetty modules are sometimes missing (e.g. `test-keystore.mod`) sometimes only referencing a link to the license, sometimes the whole license text is pasted in the `[license]` section.

We need to decide on what we should do (link or whole text) and be consistent.