Use `{cid}` as a placeholder for `IPFS_PUBLIC_GATEWAY` environment variable instead of `${cid}`

[Neurone]

Problem description

When using the ${cid} placeholder in the IPFS_PUBLIC_GATEWAY environment variable, developers must be careful to use single quotes instead of double quotes when specifying the value, otherwise in some contexts the ${cid} will be interpreted as the value of the cid environment value, resulting in an invalid value being passed to the system.

For example, if I set:

IPFS_PUBLIC_GATEWAY="https://ipfs.io/ipfs/${cid}"

The value of the env variable after the process is started will be https://ipfs.io/ipfs/ and not https://ipfs.io/ipfs/${cid} anymore.

Requirements

Use {cid} instead of ${cid} as a placeholder for the CID in the definition of the IPFS_PUBLIC_GATEWAY environment variable.

Definition of done

Developers don't need to worry about using single or double quotes when defining the values of the environment variables in the env configuration files.