Add a dedicated configuration/authentication doc covering password and access-token setup,
including environment-variable mappings and token-generation example.
Link to it from configuration docs and align the sample config wording with Matrix Authentication Service/OIDC terminology.
This is a huge patch which does some major refactoring like:
- renaming "Image Generation" to "Image Creation" in most places,
to better match its new command (`!bai image create`)
- relocating image creation command (`!bai image` -> `!bai image create`),
so it wouldn't conflict with the new image editing command (`!bai image edit`)
- introducing a new image editing command (`!bai image edit`), which
is meant to work only with the OpenAI provider, but doesn't fully work yet
due to https://github.com/64bit/async-openai/issues/364, though a next patch will fix it
- adding support for reading images off of Matrix conversations and forwarding them to
text conversations. Works for OpenAI, but not for Anthropic yet
(requires custom patches) and not for OpenAI-Compat (no support for
images there)
- relocating some utils around (base64, mime)
