Add cdt-lsp latest URL to available software sites

[jonahgraham]

To enable getting updates to users before the next SimRel we should add cdt-lsp to available software sites like we do for CDT:

This is how it is done for CDT:

https://github.com/eclipse-cdt/cdt/blob/8ac94b675f93fbcaccbedc5ca83903e7d438570b/releng/org.eclipse.cdt-feature/p2.inf#L1-L3

Remember to include the p2.inf (if new) in build.properties

https://github.com/eclipse-cdt/cdt/blob/f70a8b35c18a21a8cfb9132ad9de84caebac0d78/releng/org.eclipse.cdt-feature/build.properties#L16

[jonahgraham]

I'll do this next week before producing RC2 if no one gets to it or objects before then

[ghentschke]

@jonahgraham I'll try to provide a PR for this today

[jonahgraham]

Leaving open until this can be tested in EPP + manual install into Eclipse.

[jonahgraham]

This change looks good:

But it introduces a new one that I should have realized before now. But I don't know if we should fix it. See #344