enable custom feed

[digi-monkey]

this feature is to allow users providing a custom script to construct a custom feeds to read.

the script is something like this:

interface CustomFeedScript {
  label: string
  key: string
  filter: async (myPublickey: string, worker: CallWorker) =>  Filter
  isValidEvent: (event: Event) => boolean
}

another interesting idea is to store this script as some sorts of codes on relay and client can fetch and executing it

[digi-monkey]

first stage

• https://github.com/digi-monkey/flycat-web/pull/305

[digi-monkey]

second stage

• https://github.com/digi-monkey/flycat-web/pull/312

[digi-monkey]

• https://github.com/digi-monkey/flycat-web/pull/467