Provide bndtools 7.1+ p2 release repositories so that oomph setups can refer to specific bndtools versions

[scottslewis]

As per discussion on #6046 and summarized by issue #6083 it would be desirable to have oomph setups contributed so that users could easily create and configure bndtools without having to separately install bndtools to Eclipse.

One requirement of using oomph setups is that there should be separate p2 repo urls for specific versions of bndtools, rather than simply the latest released version of bndtools by new versions. This need is summarized by this discussion:

https://bnd.discourse.group/t/specific-release-url-for-each-release-humble-request/289

This will require some changes to the bnd build and perhaps usage of p2 director (command line)? There is relevant work described by this comment #6046 (comment)

[chrisrueger]

Just for further reference: The bnd release process (including the P2 repo stuff) seems to be described here:
https://github.com/bndtools/bnd/wiki/Release-Process