feat: Make it easier to login with email or authData

[cbaker6]

New Pull Request Checklist

• [x] I am not disclosing a vulnerability.
• [ ] I am creating this PR in reference to an issue.

Issue Description

The login method currently doesn't except a password or authData. The workaround is to create an instance of ParseUser and add any properties.

Approach

Add email and authData as optional parameters. Make the already provided parameter, username optional.

TODOs before merging

• [x] Add tests
• [x] Add changes to documentation (guides, repository pages, in-code descriptions)

[codecov[bot]]

Codecov Report

Merging #67 (3351c7b) into main (62eee27) will decrease coverage by 0.02%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #67      +/-   ##
==========================================
- Coverage   90.47%   90.46%   -0.02%     
==========================================
  Files         166      166              
  Lines       14952    14955       +3     
==========================================
+ Hits        13528    13529       +1     
- Misses       1424     1426       +2     

Impacted Files	Coverage Δ
Sources/ParseSwift/Objects/ParseUser+async.swift	94.28% <100.00%> (+0.04%)	:arrow_up:
Sources/ParseSwift/Objects/ParseUser+combine.swift	95.91% <100.00%> (+0.05%)	:arrow_up:
Sources/ParseSwift/Objects/ParseUser.swift	90.78% <100.00%> (-0.02%)	:arrow_down:

... and 3 files with indirect coverage changes

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