Implement generic Sed rule
Add DetermineEffectiveHaikuRevision rule

Simplifies PreprocessPackageInfo a bit.
Move creating the Haiku repo info to jam

* PreprocessPackageInfo rule: Pull out new rule
PreprocessPackageOrRepositoryInfo which does the sed substituation and
optionally the filtering through the C preprocessor.
* HaikuRepository rule: Generate the repository info file (from the
given template). No longer do that in the build_haiku_repository
script.
create_repository_config: Make URL argument optional

If not specified, the URL from the repository info is used.
RepositoryConfig rule: Make a bit more generic

Instead of the repository the URL can now be passed. It can use the
"$version" placeholder, which will be replaced by the content of the
given version file. If the URL is not given, the one from the repository
info will be used.
Add repository config for the Haiku repository to the image

* HaikuRepository rule: Create the repository config.
* HaikuImage: Add the repository config for the Haiku image. The
repository cache is not added, though (it would only be available, if
the repository had been built before).

Implements #10287. The Haiku repository is now available in Haiku by
default.