UserPairlist handler to manage "Manual" pairlists

[xmatthias]

Describe the enhancement

we could have a UserPairlist (name to define - this one is probably not good) pairlist, which will either provide a full pairlist (simliar to staticpairlist) - or inject additional pairs to the pairlist.

This UserPairlist get's the pairlist from a (new) database table - allowing full control to RPC by adding and removing pairs from this userpairlist at will (it's empty by default, but persisted across restarts by beeing in the database).

as the pairlist is refreshed quite often (once every iteration, unless the pairlist implements some caching) - users could simply add / remove your pair, and it'd magically appear without changing configuration or whatever.

obviously blacklist (and such) will still apply as usual, so you can't whitelist pairs that are in a blacklist - but that shouldn't really be a problem i'd hope.

It can act as both a "generator" (first position of the pairlists) - or as filter (which will add the pairs in it's list).

[aiforinvesting]

@xmatthias
How come this does not work; providing all USDT pairs in the whitelist of config.json. and populating indicator is the default RSI.

def populate_buy_trend(self, dataframe: DataFrame, metadata: dict) -> DataFrame:
    """
    Based on TA indicators, populates the buy signal for the given dataframe
    :param dataframe: DataFrame populated with indicators
    :param metadata: Additional information, like the currently traded pair
    :return: DataFrame with buy column
    """
    tickers = []
    with open('tickers.txt', 'r') as filehandle:
        for line in filehandle:
            # remove linebreak which is the last character of the string
            ticker = line[:-1]
            # add item to the list
            tickers.append(ticker)

    dataframe.loc[
        (
            # Signal: RSI 
            (dataframe['rsi'] > 0)  &
            (metadata['pair'] in tickers)
        ),
        'buy'] = 1

    return dataframe

[xmatthias]

I guess this approach could work (assuming you have no bugs) - but it's not what this issue is about, but about providing a way to manage the pairlist "online" - either via API or via telegram.

Investigating why your code will or will not is however clearly not part of this issue.

[epigramx]

The dream would be to have full (and easy) programmatic freedom. But I wonder if a good first version is an EditPairList that can be set at the end of the chain and it has only three string settings: append; prepend and remove.
So for example after one uses all the current filters as normal at the end it would have "remove these pairs" or/and "append these pairs" and/or "prepend these pairs".