Increase the `max_length` of the `description` field of `Reference` or make them `TextField`s

[Zethson]

Add a description

It currently uses the default value of 255. However, some CELLxGENE collection descriptions have more than 255 characters.

[falexwolf]

I meanwhile think that the pro for an unlimited description field (user can put whatever they want) outweigh the cons (more predictable behavior for UI display, less db resources, faster queries). So, I suggest we consistently make them TextFields and thereby remove the length limitation.

[falexwolf]

For keys I suggest we increase the limit to 1024 chars consistent with what Claude says S3 uses.

[Zethson]

Fixed in #3109