Add sort field to evalutor result filterset

[willbarton]

This adds a sort field to the evaluator results filterset. From the evaluator results endpoint in the API this should enable sorting, either ascending (with just the sort field) or descending (prefixing the sort field with -), on any of the listed fields (which are those available from AccountActivity).

This leverages the existing django-filters filter set by adding an [OrderingFilter field](https://django-filter.readthedocs.io/en/stable/ref/filters.html#django_filters.filters.OrderingFilter

For example, the query arguments ?view=all&sort=-activity_date would sort by activity descending.

To sort on multiple fields, they can be separated by comma, for example: ?view=all&sort=-activity_date,current_bal will sort by activity date descending (newest first) and by current balance ascending (lowest first).

Once merged, I will add the following to the API wiki page's section on the evaluator results view:

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If the sort parameter is given the results will be sorted by the given field(s) either ascending (using the field name without decoration) or descending (prefixing the field name with -). Multiple fields can be sorted by comma-separating them. Fields the results can be sorted on are:

• activity_date
• cons_acct_num
• port_type
• acct_type
• date_open
• credit_limit
• hcola
• id_num
• terms_dur
• terms_freq
• smpa
• actual_pmt_amt
• acct_stat
• pmt_rating
• php
• php1
• spc_com_cd
• compl_cond_cd
• current_bal
• amt_past_due
• orig_chg_off_amt
• doai
• dofd
• date_closed
• dolp
• int_type_ind
• account_holder__cons_info_ind
• account_holder__ecoa
• account_holder__cons_info_ind_assoc
• account_holder__ecoa_assoc
• k2__purch_sold_ind
• k2__purch_sold_name
• k4__balloon_pmt_amt
• l1__change_ind
• l1__new_id_num
• l1__new_acc_num

For example, ?view=all&sort=-activity_date,current_bal will sort by activity date descending (newest first) and by current balance ascending (lowest first).

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Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Passes all existing automated tests

[virginiacc]

@willbarton This looks great! 🎉

Looking at the list of fields, I realized I forgot about the consumer account number column in the evaluator results table when we were discussing which fields should be sortable. Would it be possible to make that one sortable too?

[willbarton]

@virginiacc added cons_acct_num to sortable fields!

[virginiacc]

Works perfectly -- thanks, @willbarton!