feat: add confluence source

[nicoloboschi]

• New confluence-source agent

- type: "confluence-source"
                                    id: "step1"
                                    configuration:
                                        username: ""
                                        api-token: ""
                                        domain: ""
                                        spaces: [""]
                                        state-storage: s3
                                        state-storage-s3-bucket: "test-state-bucket"
                                        state-storage-s3-endpoint: "%s"
                                        deleted-objects-topic: "deleted-objects"
                                        idle-time: 1
                                        root-parents: [""]

Fields:

• username: the connector uses basic auth, you need to put your user email
• api-token: Generate an api token from here https://id.atlassian.com/manage-profile/security/api-tokens
• domain: Domain of the confluence instance (e.g. vectorize.atlassian.net)
• spaces: List of spaces to read pages from. Space might be the internal id (numeric), the Display name or the key (that you get from the URL in the browser)
• root-parents: instead of reading the whole space, you can filter by root pages (must be the numerical ids that you can find in the URL in the browser)

The exported content is in HTML format using confluence export method.
The checksum is not computed but we use the page version (which normally means something has changed in the content)