Docs updates - Githubissues

Closes #220

Changes proposed in this Pull Request

Thanks for getting a bunch of this done, @ktehranchi! My updates are:

Updated the sector wildcards section
On the retirement, it was set up like it was a subdictionary under electricity. So I fixed that.
Load is removed in upcoming PR #288 and replaced by scale.
OperationalReserves added following PyPSA-Eur docs
Added demand config following updates from PR #202
Added autarky following PyPSA-Eur docs
Removed co2_monthly_prices as that pulled historical data for Europe model
Fixed sector config options
Move interconnect co2 base values to its own unlisted page

[x] I tested my contribution locally and it seems to work fine.
[x] Code and workflow changes are sufficiently documented.
[x] Changed dependencies are added to envs/environment.yaml.
[x] Changes in configuration options are added in all of config.default.yaml.
[x] Changes in configuration options are also documented in doc/configtables/*.csv.