feat: add FeaturesProxy integration for feature flag management in CMS and LMS #922

Job	Run time
run_ci (ubuntu-24.04, 3.11, registrar+lms)	17m 51s
run_ci (ubuntu-24.04, 3.11, discovery+lms+forum)	27m 48s
run_ci (ubuntu-24.04, 3.11, ecommerce+lms)	21m 13s
run_ci (ubuntu-24.04, 3.11, analyticsapi+insights+lms)	25m 17s
run_ci (ubuntu-24.04, 3.11, edx_notes_api+lms)	19m 19s
run_ci (ubuntu-24.04, 3.11, credentials+lms)	18m 19s
run_ci (ubuntu-24.04, 3.11, enterprise-subsidy+enterprise-catalog+enterprise-access+lms)	25m 59s
run_ci (ubuntu-24.04, 3.11, designer+lms)	22m 10s
run_ci (ubuntu-24.04, 3.11, edx-exams+lms)	20m 26s
run_ci (ubuntu-24.04, 3.11, license-manager+lms)	19m 28s
run_ci (ubuntu-24.04, 3.11, xqueue)	3m 26s
	3h 41m 16s

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