[PROPOSAL] Feed primary key field with sequence.nextval and foreign key with sequence.currval

## Context

We have to insert the jsonobject in a table film

```
{
"film_id": 452
"title" : "The Matrix"
"year": 1999
}
```

## Problem

During a dataset insert primary key have to be unique to avoid conflict with existing values. Also sequences have to be updated upper than the maximum primary key inserted to avoid future conflict.

## Solution

Add sequence information in `table.yaml` and use it during `lino push insert` process.

```yaml
version: v1
tables:
- name: film
keys:
- film_id
sequence :
film_id: sequence_film_id
```

If the `film_id` is omitted, lino use the value of `sequence_film_id.nextval` to feed the primary_key.

## Relation

If the primary key is a part of a relation

```yaml
- name: film_film_category
parent:
name: film
keys:
- film_id
child:
name: film_category
keys:
- film_id
```

inserting the following JSON object

```json
{
"title" : "The Matrix",
"year": 1999,
"film_film_category" : [
{
"category_id": 151
},
{
"category_id": 452
},
]
}
```

will produce the sql statements

```sql
insert into film (film_id, title, year)
values (sequence_film_id.nextval, 'The Matrix', 1999);
insert into film_category (film_id, category_id)
values (sequence_film_id.currval, 151 );
insert into film_category (film_id, category_id)
values (sequence_film_id.currval, 452 );
```