qmc-fit help keys are auto-populated correctly

[shivupa]

Proposed changes

A minor fix that autogenerates the valid keys for qmc-fit.

# Before
  -f FIT_FUNCTION, --fit FIT_FUNCTION
                        Fitting function, options are []. (default: linear)
# After
  -f FIT_FUNCTION, --fit FIT_FUNCTION
                        Fitting function, options are ['birch', 'cubic',
                        'linear', 'morse', 'murnaghan', 'quadratic',
                        'quartic', 'sqrt', 'vinet']. (default: linear)

What type(s) of changes does this code introduce?

• Bugfix

Does this introduce a breaking change?

• No

What systems has this change been tested on?

local workstation

Checklist

• Yes. This PR is up to date with current the current state of 'develop'
• No. Code added or changed in the PR has been clang-formatted
• No. This PR adds tests to cover any new code, or to catch a bug that is being fixed
• No. Documentation has been added (if appropriate)

[prckent]

Thank you

[prckent]

Test this please

[ye-luo]

Test this please