ref(users): move users related web resources to users directory

[Christinarlong]

Moves user related web resources and adds typing where needed.

• user_avatar & test_user_avatar
• accounts & test_accounts
• forms/accounts -> split into users/web/accounts_form.py & web/forms/accounts.py for user and auth related resources
• tests/forms/test_accounts.py -> tests/users/web/account_forms.py (only contains user resource related tests so not split)
• account_identity & test_account_identity

ref(issue # here)

[codecov]

Codecov Report

Attention: Patch coverage is 86.08696% with 16 lines in your changes missing coverage. Please review.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/sentry/users/web/accounts_form.py	80.51%	13 Missing and 2 partials ⚠️
src/sentry/users/web/accounts.py	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #76981      +/-   ##
==========================================
+ Coverage   78.22%   78.25%   +0.02%     
==========================================
  Files        6898     6901       +3     
  Lines      306690   307146     +456     
  Branches    50276    50326      +50     
==========================================
+ Hits       239913   240344     +431     
- Misses      60415    60427      +12     
- Partials     6362     6375      +13     

[markstory]

Nice job consolidating this with its clone 👏