LogtailHandler: Do not expect "host" parameter to include protocol

[PetrHeinz]

Previously, host needed to include the https:// which is unintuitive:

from logtail import LogtailHandler
import logging

handler = LogtailHandler(
    source_token='$SOURCE_TOKEN', 
    host='https://in.logs.betterstack.com',
)
logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
logger.handlers = []
logger.addHandler(handler)

Now, we should also support just ingesting host being sent, as noted in #31:

from logtail import LogtailHandler
import logging

handler = LogtailHandler(
    source_token='$SOURCE_TOKEN', 
    host='in.logs.betterstack.com',
)
logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
logger.handlers = []
logger.addHandler(handler)