add dropdown menu to download stacker analytics

[hbdc-BtcFixesThis]

Description

#2612

To avoid data formatting json download was chosen. This allows the user access to the data as its used to populate the charts for them to restructure as they see fit.

Screenshots

Additional Context

Was anything unclear during your work on this PR? Anything we should definitely take a closer look at?
No. I wasn't sure where to add sample data files that are generated when clicking download so I thought I'd add them here.

endpoint (six downloads for all charts exposed):
registration_growth.txt
spending_growth.txt
spender_growth.txt
item_growth.txt
stacking_growth.txt
stacker_growth.txt

endpoint (two downloads for two charts exposed): /stackers/bitcoin/month
revenue_growth_subs.txt
item_growth_subs.txt

Checklist

Are your changes backward compatible? Please answer below:
Yes

On a scale of 1-10 how well and how have you QA'd this change and any features it might affect? Please answer below:
8

For frontend changes: Tested on mobile, light and dark mode? Please answer below:
Yes

Did you introduce any new environment variables? If so, call them out explicitly here:
No

Did you use AI for this? If so, how much did it assist you?
No

[ed-kung]

Not a big deal, but I would still recommend CSV over JSON, since I think it'd be more accessible to more people, especially the users who might make use of this feature most.

[hbdc-BtcFixesThis]

Thanks for the feedback @ed-kung. I added the option to download as csv and would be happy to remove the json option if it clutters the screen or is unhelpful etc. Here are some screenshots and the results of csv downloads

revenue_growth_subs.csv
item_growth_subs.csv
item_growth.csv
registration_growth.csv
spending_growth.csv
spender_growth.csv
stacking_growth.csv
stacker_growth.csv