Blobs upload proposal

Nobody has claimed this yet.

1) send sdblob in this format:
```
type request struct {
hash string
sdblob []byte
}
```
2) server checks the blocklist to see if it wants the stream
3) server checks if the sdblob is already in our system
3.1) if the sd blob exists, respond with a list of blobs it needs
3.2) if the sd blob doesn't exist, store the sd blob, save the blobs in the DB with is_stored=0, respond with a list of the blobs it needs (all of them)
4) client sends one blob at a time with the following format
```
type request struct {
hash string
blob []byte
size int
}
```
5) server checks that the uploaded blob has the correct hash and size, saves the blob to S3, sets is_stored=1 in the database, responds with a success
6) optionally we should add an endpoint that accepts a list of sdblob hashes and returns whether the sdblob is needed or not and if the sdblob is already stored, a list of blobs that are missing
the server thus has to implement the following endpoints:
`/sdblob POST`
accepts:
```
type request struct {
hash string
sdblob []byte
}
```
returns:
```
type response struct{
success bool
error *error
type data struct {
required_blobs []string
}
}
```
`/blob POST`
accepts:
```
type request struct {
hash string
blob []byte
size int
}
```
returns:
```
type response struct{
success bool
error *error
}
```
`/sdblobs POST`
accepts:
```
type request struct {
hashes []string
}
```
returns:
```
type response struct{
success bool
error *error
type data struct {
required_sdblobs []string
required_blobs []struct{
sdhash string
missing_blobs []string
}
}
}
```

Start by locating the server entry points for the /sdblob, /blob, and /sdblobs POST endpoints, then inspect the blocklist, database, and S3 integrations. Done means the three request and response flows implement the listed checks, blob-state updates, missing-blob responses, and hash and size validation.

Written by the indexing model from the issue text.