[EEG Browser] Add ability to view annotations in event panel and overlaid on signal viewer

[jesscall]

Brief summary of changes

Disclaimer: This PR is blocked by #7811 and will need to be rebased after its merge.

The changes in this PR fill in a few gaps in the code and allow for annotation data to be viewed in the EEG Browser. Annotations are displayed in orange in the Events / Annotation Panel and when selected are shown as an overlay in the signal viewer.

Testing instructions (if applicable)

1. Reach out to @jesscall on slack to get access to annotation data / SQL patches
2. Insert the SQL into your DB and place the files on your VM.
3. Navigate to the EEG Browser
4. Make sure that you can see and interact with annotations data.

[christinerogers]

For clarification - does this commit Laetitia's atlas code to main, or is it your new fixes on top of that ?

[jesscall]

@christinerogers

Laetitia's ATLAS code fetches the annotations data from the annotation.tsv file.

Since @AlexandraLivadas 's PR #7433 was merged adding back-end structure for annotations, I implemented a solution that gets the info from the DB tables rather than reading from the tsv file.

TLDR; The code in this PR is inspired by ATLAS code, but has a different implementation.

Hope that's clear?

[jesscall]

@christinerogers Also for clarification: adding new annotations via front-end is not part of this PR. There are still gaps in the code. PR for that coming soon.

[jesscall]

rebased, no longer blocked

[laemtl]

Replaced by #8235