Implement missing user directory features

[matrixbot]

This issue was originally created by @kegsay at matrix-org/dendrite#1330.

Sytests:

    × Users appear/disappear from directory when join_rules are changed
    × Users appear/disappear from directory when history_visibility are changed
    × Users stay in directory when join_rules are changed but history_visibility is world_readable

[matrixbot]

This comment was originally posted by @kegsay at matrix-org/dendrite#1330 (comment).

Still failing as of today.

[matrixbot]

This comment was originally posted by @apatelKmd at matrix-org/dendrite#1330 (comment).

I want to work on the issue.
I am new to the project and need more details on what needs to be done. Can someone help?