fix: moving hl.init

[Daniel-Considine]

✨ Context

Currently we initialise hail (hl.init()) at the start of any steps that require it.
The behaviour of hail (v0.2.127) currently doesn't check if hail is already initialised. This means running the step again will cause hail to attempt to initialise another hail session and crash.

🛠 What does this PR implement

This PR makes it so that when start_hail is True at session creation, hl.init() is automatically ran. As a result it says in sync with the current spark session.

🙈 Missing

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[ireneisdoomed]

LGTM! Thank you. Having this inside session makes more sense. Just remember to erase the hail init in gnomad_ingestion

[d0choa]

There are 3 hl.init in the notebooks:

• FineMapping_AlzheimerDisease.ipynb
• Mapping_EFO_finngen.ipynb
• Productionizing_LD_matrix.ipynb

Rest makes sense