[RFC 0127] Nixpkgs "problem" infrastructure (NixOS#127)

* [RFC 0127] Nixpkgs issues and warnings (NixOS#127)

* Add URLs as structured information

* Update rfcs/0127-issues-warnings.md

Co-authored-by: Linus Heckemann <[email protected]>

* Update rfcs/0127-issues-warnings.md

Co-authored-by: Linus Heckemann <[email protected]>

* Update rfcs/0127-issues-warnings.md

Co-authored-by: Linus Heckemann <[email protected]>

* Update rfcs/0127-issues-warnings.md

Co-authored-by: Linus Heckemann <[email protected]>

* Update rfcs/0127-issues-warnings.md

Co-authored-by: Linus Heckemann <[email protected]>

* Update rfcs/0127-issues-warnings.md

* RFC 127 update shepherds

* RFC 127 rework

* Point out that the previous warnings system was not documented

* Rework ignore mechanism

* Update rfcs/0127-issues-warnings.md

Co-authored-by: Silvan Mosberger <[email protected]>

* Update rfcs/0127-issues-warnings.md

Co-authored-by: Silvan Mosberger <[email protected]>

* Remove "resolved" attribute again

* Incorporate review feedback

* Rewrite (again)

* Rename throw->error, trace->warn

* Make meta.problems an attrset

* Rewrite *again*, most change is in the configuration options

* Review update (WIP)

* Review update

* Update shepherds list

* Meeting update

* Typos

---------

Co-authored-by: Linus Heckemann <[email protected]>
Co-authored-by: Silvan Mosberger <[email protected]>