Added "signature" field to bLIP-10 tlv spec

[daveajones]

A signature field to allow signing by the sender to verify their identity.

https://github.com/Podcastindex-org/podcast-namespace/blob/main/value/blip-0010.md#fields

[brianoflondon]

Funnily enough we must have originally had a field called signature in there because when I was updating things today in my python (2 year old code!) there was already a signature item in my data structure. The only new ones I put in today are the reply_ ones at the end.

class KeysendCustomRecord(BaseModel):
    podcast: Optional[str]
    feedID: Optional[int]
    url: Optional[AnyUrl]
    guid: Optional[UUID]
    #
    episode: Optional[str]
    itemID: Optional[int]
    episode_guid: Optional[str]
    #
    time: Optional[str]
    ts: Optional[int]
    action: Optional[str] = "stream"
    app_name: Optional[str] = "unknown"
    app_version: Optional[str]
    boost_link: Optional[str]
    message: Optional[str]
    name: Optional[str]
    pubkey: Optional[str]
    sender_key: Optional[str]
    sender_name: Optional[str]
    sender_id: Optional[str]
    sig_fields: Optional[str]
    signature: Optional[str]
    speed: Optional[str]
    uuid: Optional[str]
    value_msat: Optional[int]
    cr_value_msat: Optional[int]
    value_msat_total: Optional[int]

    reply_lnaddress: Optional[str]
    reply_address: Optional[str]
    reply_custom_key: Optional[str]
    reply_custom_value: Optional[str]