Do not use wandb if not specified in the config file

[jcohenadad]

Checklist

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• I've linked relevant issues in the PR body
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PR contents

• I've consulted ivadomed's internal developer documentation to ensure my contribution is in line with any relevant design decisions
• I've added relevant tests for my contribution
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Description

#1252, even if the config file does NOT include any wandb field, training with ivadomed can use wandb in case wandb logging was previously done, indicates that deliberate omission of the value to wandb_api_key while logging in and the anonymous logging feature introduced in #1193 could sometimes be misleading and undesired. Hence, this PR undoes and simplifies it by bypassing wandb.login call if the key is not defined or is empty.

Linked issues

Resolves #1252

[coveralls]

Pull Request Test Coverage Report for Build 3933753469

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 74.114%

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Totals
Change from base Build 3915337488:	0%
Covered Lines:	4621
Relevant Lines:	6235

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💛 - Coveralls

[jcohenadad]

@kanishk16 do you mind reviewing this? if you cannot please let me know

[kanishk16]

I'm sorry to stall the progress... On it right away... weirdly all the notifications were sent to my spam

[kanishk16]

#1252 indicates that deliberate omission of the value in wandb_api_key while logging in and the anonymous logging feature introduced in #1193 could sometimes be misleading and undesired. Hence, this undoes and simplifies it.

We'd also like to remove this from the documentation here. Specifically, the following should be removed from the docs:

From then on, the value in this key-value pair in the config file could be omitted, like 'wandb_api_key': ''

[jcohenadad]

We'd also like to remove this from the documentation here. Specifically, the following should be removed from the docs:

Yes! excellent catch

[kanishk16]

LGTM 🚀 Will merge once tests pass!