Add option to change xTB parameterisation version and temperature

[shoubhikraj]

Adds options to change the xTB --etemp and --gfn flags from Config. Default values (None) prevent use of those flags.

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Checklist

• [x] The changes include an associated explanation of how/why
• [x] Test pass
• [x] Documentation has been updated
• [x] Changelog has been updated

[codecov[bot]]

Codecov Report

Merging #252 (d251e28) into v1.4.0 (5f355e7) will decrease coverage by 0.08%. The diff coverage is 97.37%.

@@            Coverage Diff             @@
##           v1.4.0     #252      +/-   ##
==========================================
- Coverage   97.34%   97.26%   -0.08%     
==========================================
  Files         195      195              
  Lines       20410    20417       +7     
==========================================
- Hits        19868    19859       -9     
- Misses        542      558      +16     

Flag	Coverage Δ
unittests	97.26% <97.37%> (-0.08%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
autode/calculations/calculation.py	99.11% <ø> (-0.21%)	:arrow_down:
autode/transition_states/transition_state.py	74.67% <22.22%> (ø)
autode/neb/original.py	95.97% <96.96%> (-1.73%)	:arrow_down:
autode/__init__.py	100.00% <100.00%> (ø)
autode/config.py	100.00% <100.00%> (ø)
autode/constraints.py	98.78% <100.00%> (+0.07%)	:arrow_up:
autode/neb/ci.py	82.60% <100.00%> (-1.84%)	:arrow_down:
autode/neb/idpp.py	100.00% <100.00%> (ø)
autode/neb/neb.py	100.00% <100.00%> (ø)
autode/opt/optimisers/dimer.py	98.03% <100.00%> (-0.02%)	:arrow_down:
... and 22 more

... and 4 files with indirect coverage changes

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[shoubhikraj]

@t-young31 Could you please merge the PR (I don't have merge access)?

[t-young31]

please let me know if you want permissions so you can merge it yourself!

[shoubhikraj]

@t-young31 Maybe later, when I get used to github a little bit more 😅