chore: use indexes instead of index_together in models

[hamadr]

index_together is deprecated and will be removed in django future

[github-actions]

🦄 coverage 100 %

Name	Stmts	Miss	Cover	Missing
dalec/__init__.py	1	0	100%
dalec/apps.py	4	0	100%
dalec/models.py	44	0	100%
dalec/proxy.py	135	0	100%
dalec/settings.py	42	0	100%
dalec/templatetags/__init__.py	0	0	100%
dalec/templatetags/dalec.py	38	0	100%
dalec/tests_utils.py	25	0	100%
dalec/urls.py	4	0	100%
dalec/views.py	123	0	100%
dalec_example/__init__.py	2	0	100%
dalec_example/apps.py	4	0	100%
dalec_example/proxy.py	60	0	100%
dalec_prime/__init__.py	2	0	100%
dalec_prime/apps.py	4	0	100%
dalec_prime/migrations/0001_initial.py	12	0	100%
dalec_prime/migrations/0001_squashed_0005_auto_20231017_1208.py	12	0	100%
dalec_prime/migrations/0002_auto_20211109_1546.py	5	0	100%
dalec_prime/migrations/0003_auto_20211109_1615.py	5	0	100%
dalec_prime/migrations/0004_alter_content_id_alter_fetchhistory_id.py	5	0	100%
dalec_prime/migrations/0005_auto_20231017_1208.py	4	0	100%
dalec_prime/migrations/__init__.py	0	0	100%
dalec_prime/models.py	7	0	100%
runtests.py	12	0	100%
TOTAL	550	0	100%

[DylannCordel]

fix #19