Implement basic CRUD operations for REST API

[s-vitaliy]

This Pull Request introduces basic CRUD operations for the following application entities:

• Policy
• External identity
• Policy attachment to external identity

Checklist

• GitHub issue exists for this change.
• Unit tests added and they pass.
• Line Coverage is at least 80%.
• Review requested on latest commit.

[github-actions]

Coverage after merging crud into main will be

4.90%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src
main.rs	0%	100%	0%	0%	22, 40–67
src/http
conversions.rs	95.65%	100%	100%	94.74%	26
urls.rs	0%	100%	0%	0%	100–110, 112–119, 12, 120–125, 127–129, 13, 130–139, 14, 141–149, 15, 150–153, 16–29, 31, 33, 35–48, 50–60, 62–72, 74–86, 88–98
src/models/external
identity.rs	0%	100%	0%	0%	16–21, 25–27, 38–40, 42–46, 49, 56–58, 60–64, 66–70
identity_provider.rs	0%	100%	0%	0%	10–11, 16–18, 9
token.rs	100%	100%	100%	100%
src/models/internal/v1
token.rs	0%	100%	0%	0%	24–33, 39, 52–55, 58–79
src/services
configuration_manager.rs	0%	100%	0%	0%	25–48, 50–52
external_identity_validator.rs	0%	100%	0%	0%	42–56, 59–67, 76–86
identity_validator_provider.rs	0%	100%	0%	0%	13–15, 46–52, 61–66, 70–73
token_service.rs	0%	100%	0%	0%	40–77, 81–93
src/services/repositories
in_memory.rs	0%	100%	0%	0%	100–103, 14–20, 26–30, 32–36, 43–49, 51–55, 57–61, 70–76, 82–97, 99