Improve developers section

[mosabua]

With the current setup any inheriting project has to override developers .. otherwise they get
the following in the effective pom:

<developers>
    <!-- see git log -->
    <developer>
        <name>Airlift</name>
    </developer>
</developers>

Which is wrong. This is currently the case in Trino for example.

The new setup pulls the scm url into place and results in a correct URL to the github or whatever repo and has a generic sentence instead of referencing airlift. Here is the effective pom for this project itself:

    <developers>
      <developer>
        <name>Numerous contributors, see scm log</name>
        <url>https://github.com/airlift/airbase</url>
      </developer>
    </developers>

It uses the property so for example in Trino we would get this:

    <developers>
      <developer>
        <name>Numerous contributors, see scm log</name>
        <url>https://github.com/trinodb/trino</url>
      </developer>
    </developers>

and in the Trino Gateway:

    <developers>
      <developer>
        <name>Numerous contributors, see scm log</name>
        <url>https://github.com/trinodb/trino-gateway</url>
      </developer>
    </developers>

Note that the property project.scm.url is filled in most cases since it is needed for Central deployment and release plugin usage.

Discovered during work on trinodb/trino-gateway#29 and requested by @dain

FYI @electrum @martint

[mosabua]

Thanks for the merge @electrum