Extend the GraphQL mutations APIs

Is your feature request related to a problem? Please describe.
Currently the Decidim GraphQL API allows mostly fetching records from the API, i.e. read-only. The only mutation/write API that we have today is for creating comments because the comments section used to work as a separate React application that utilized this API.

The write APIs (i.e. GraphQL mutations) are missing for most records although they would be highly useful for many integration purposes.

Describe the solution you'd like
I would like to have the following mutation APIs available for the different records within Decidim:

• Proposals
• Answer a proposal / update the answer for a proposal
• Budgets
• CRUD budget
• CRUD project
• Accountability
• CRUD result
• CRUD timeline entry

In addition, we also need API credential management and login/logout endpoints for the APIs that work programmatically.

Describe alternatives you've considered
Creating a one-off mutations that serve a specific purpose (e.g. one of the operations listed above) but this is not very maintainable or scalable way to develop the platform further. We would see these APIs to be beneficial also for the core.

Additional context
We have a project in progress where we actually need these APIs, so this is just to communicate to the product team that we will be working on creating these APIs.

We will initially create these APIs in a separate module because we need them already for the current 0.27 version but we would like to integrate these eventually also to the core.

Does this issue could impact on users private data?
No

Funded by
We have a customer who is funding the project