Cardano Updates

2468: Replace `hardfork_at` with `eras` object r=Anviking a=Anviking

# Issue Number

ADP-676


# Overview

<!-- Detail in a few bullet points the work accomplished in this PR -->

- [x] Replace `hardfork_at` with info of all eras
- [x] Instead of storing ProtocolParameters in DB, just keep them in a `TVar`
- [ ] <s>See if we can order the eras correctly in the `era` object (for when the JSON is viewed by humans)</s> Seems impossible to do.
- [x] TODO: Extend swagger
- [ ] Tiny doc tweaks

# Comments

- Could add absolute `slot` field also
- Arguably a bit sad that the eras get sorted seemingly alphabetically in the json

```json
$ cardano-wallet network parameters
{
    "slot_length": {
        "quantity": 1,
        "unit": "second"
    },
    "decentralization_level": {
        "quantity": 74,
        "unit": "percent"
    },
    "genesis_block_hash": "5f20df933584822601f9e3f8c024eb5eb252fe8cefb24d1317dc3d432e940ebb",
    "blockchain_start_time": "2017-09-23T21:44:51Z",
    "desired_pool_number": 500,
    "epoch_length": {
        "quantity": 432000,
        "unit": "slot"
    },
    "eras": {
        "shelley": {
            "epoch_start_time": "2020-07-29T21:44:51Z",
            "epoch_number": 208
        },
        "mary": null,
        "byron": {
            "epoch_start_time": "2017-09-23T21:44:51Z",
            "epoch_number": 0
        },
        "allegra": {
            "epoch_start_time": "2020-12-16T21:44:51Z",
            "epoch_number": 236
        }
    },
    "active_slot_coefficient": {
        "quantity": 5,
        "unit": "percent"
    },
    "security_parameter": {
        "quantity": 2160,
        "unit": "block"
    },
    "minimum_utxo_value": {
        "quantity": 1000000,
        "unit": "lovelace"
    }
}
```

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Co-authored-by: Johannes Lund <[email protected]>

We never want to use the old genesis parameters just because the wallet
just started.

The onTipUpdate will be run immediately on startup, and will fetch
both interpreter, and protocol parameters.

To be safe, and for readability, let's replace the TVar+initial val with
an empty TMVar though.

Use relative path of cnode.sh instead of hard coded default
Only match against port to get cnode PID

Co-authored-by: Ola <[email protected]>