perf: adding a source faster compatibility source for eox-tenant

[felipemontoya]

Description

This PR adds a new config source. This source is a faster implementation of the microsite_V0.

• V0, will remove a key that is unused by the current version of control center and will then pass that call to configuration_helpers.
• V1 will not remove the key.
• V2 will remove the key, but then make a faster call to django settings directly.

Testing instructions

first, add the following config to lms.env.json:

"EOX_THEMING_CONFIG_SOURCES":[
  "from_eox_tenant_microsite_v2",
  "from_django_settings"
],

when using a profiler, the call went from:

Per call: 6.056e-05 | config_sources.py:42(from_eox_tenant_microsite_v0)

to

Per call: 7.453e-06 | config_sources.py:51(from_eox_tenant_microsite_v2)

One order of magnitude faster.

Checklist for Merge

• Tested in a remote environment -> I suppose you need to apply this in order to test @Alec4r
• Updated documentation N/A
• Rebased master/main N/
• Squashed commits N/