[synapse] use python virtual environment

[skowalak]

Hello 👋🏻 , I would like to make some changes to the Synapse guide.

1. Use a virtual python environment instead of installing the packages with --user.
2. Remove dependency psycopg2 in favor of psycopg2-binary, because currently the update process is broken (see #1265)

Also I have a question: I would like to add a guide for setting up an Appservice along with synapse, for example a mautrix bridge. Should that be a separate guide, or a new section in the synapse guide? The process is pretty much the same for Synapse and Dendrite by my own experience.

Looking forward to hearing from you!

[noave]

Should that be a separate guide, or a new section in the synapse guide?

I would say it depends on the complexity, if its done in some codeblocks, go for a section. But I guess as there is more complexity within it, this should be a separate guide and could be linked from there