select correct sector name in endogeneous retrofitting

[martacki]

Changes proposed in this Pull Request

Turns out we're making this PR bigger and include many more fixes than originally intended:

• selection of the sector sec never chose services, thus costs of retrofitting services were highly overestimated (on average by a factor of 4). Fixed by correctly defining the corresponding variable sec
• introduced a more general node name that allows more than 9 buses per synchronous region
• avoiding deprecation of .groupby(axis=1) and not using .loc[]
• discriminate between district heating, decentral heating in urban areas or rural areas for floor_area_node calculations
• discriminate between gas boilers and resistive heaters in configuration (config.default.yaml), default settings align with previous settings
• remove gas generators in sector network if gas is a carrier (only gas store allowed)

Checklist

• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in all of config.default.yaml.
• Changes in configuration options are also documented in doc/configtables/*.csv.
• A release note doc/release_notes.rst is added.

[fneum]

Most changes look good. Thanks @martacki.

I am just unsure about skipping the gas generator. Wouldn't that mean the model can't use fossil gas anymore?

[fneum]

Suggested change

	if carrier == "gas":
	return

This would prohibit the use of fossil gas, wouldn't it?

Since the store is cyclic, where would the model source fossil gas?

[fneum]

I merged without removing the gas generators. Feel free to amend in another PR if necessary.