ExerciseStyle.EUROPEAN contracts aren't reported by TradingClient

[jimwhite]

Describe the bug
The Option Market Data API supports euro-style options but the Trading API does not. It's not (yet) a problem for us that trading in euro-style options isn't supported (we also need L3 which I understand is in the works) but we need the contract data for other things like algo development.

To Reproduce
Get an option chain for a euro-style option.

OptionHistoricalDataClient.get_option_chain(OptionChainRequest(underlying_symbol="XSP"))

That works as expected, like:

{'XSP240513C00480000': {   'greeks': None,
     'implied_volatility': None,
     'latest_quote': {   'ask_exchange': '?',
...

Try to get the contract details for any of those symbols:

TradingClient.get_option_contract(symbol_or_id='XSP240513C00480000')

That fails like this:

APIError: {"code":40410000,"message":"option contract XSP240513C00480000 not found"}

Expected behavior
Even if Alpaca doesn't support trading of euro-style options (yet), we still need the data in order to develop algos in anticipation of them being supported.

So either of:

1. TradingClient.get_option_contract and get_option_contracts calls should work when style is ExerciseStyle.EUROPEAN.

2. We need to have those functions in the OptionHistoricalDataClient too in order to provide data on options even if they can't be traded.

[grzesir]

This would be great to have