Way to manage current available plugins #6299
Description
What would you like to be added:
We need a list of available PipeCD plugins (including versions) so that users can explore them when working with piped plugins.
Some idea:
- List in pipe-cd/pipecd repo README
- New docs category in pipecd.dev/docs
Requirement:
- Low maintenance cost: the list must be up to date with less managing resources
- Easy to find and access
Why is this needed: