Rewrite Pipeline in go

[KruseTim]

To make the pipeline more performant and make the backend consistent, rewrite the pipeline in go.
In doing so, we will introduce

• parallelization of i2t request and similarity processing
• remove unneeded functionality

[v4lli]

Besides improved parallelism, I think structuring the pipeline in a staged manner (i.e. similar to how CPU instruction pipelining works https://en.wikipedia.org/wiki/Instruction_pipelining) could make sense from a code perspective as well. This would help with both code organization (every stage = single function with clearly defined inputs and outputs) as well as running the stages concurrently