cleanup infra for background tasks

[rchincha]

Is your feature request related to a problem? Please describe.

Here are the requirements for background tasks:

1. Cannot aggressively hold storage locks since HTTP threads must be prioritized - interactive vs background jobs
2. Single place to handle this.
3. Make it easy for multiple extensions/features to use this.
4. We expect embedded device use cases as well, so memory usage should be minimal

Describe the solution you'd like

Pls. look at: https://gobyexample.com/tickers https://github.com/go-co-op/gocron

[rchincha]

Also, as an iterator over repos, the two options are:

1. repos = get_all_repos(); foreach repo := repos { // do something }

The issue is that "repos" can become quite large and will this work on a raspberry pi, for example

2. for repo = get_first_repo(); repo = get_next_repo(repo) { // do something }

A first/next iterator consumes more CPU potentially, but memory usage is small.

[rchincha]

Also, always be clear about interactive and background tasks. Interactive tasks (HTTP threads) are highest priority and background tasks whenever possible must not degrade QoS for interactive tasks.