feat: Introduce special header that tells Loki not to modify query results

[MasslessParticle]

This PR introduces the new LokiOriginalResults header and ensures it's propagated to any component that could modify query results.

[ashwanthgoli]

i think the querier change here only handles requests directly made to queriers http endpoint.

for requests that pass through schedulers, i believe we are encoding these headers within the request itself.
for protobuf encoding and json encoding

[MasslessParticle]

ty, good catch

[grafanabot]

Hello @MasslessParticle!
Backport pull requests need to be either:

• Pull requests which address bugs,
• Urgent fixes which need product approval, in order to get merged,
• Docs changes.

Please, if the current pull request addresses a bug fix, label it with the type/bug label.
If it already has the product approval, please add the product-approved label. For docs changes, please add the type/docs label.
If the pull request modifies CI behaviour, please add the type/ci label.
If none of the above applies, please consider removing the backport label and target the next major/minor release.
Thanks!

[grafanabot]

This PR must be merged before a backport PR will be created.