fix: handle different vault injection cases

[csatib02]

Overview

• The injector already utilizes a bunch of things, to detect vault secret references.
• On the side of secret-init it's sufficient if we use a regex to detect vault:something/something/... like substrings in the env-values, since it won't mistake vault like env-values for vault references, and if somehow a non-vault reference would be detected, the injector would just ignore it.
• Added an e2e test case to test different injection scenarios.

Fixes #68

[ramizpolic]

The test scenario in env_store_test.go could be a bit changed to set envs itself, for example rather than using createEnvsForProvider helper function, we could set envs in the test cases explicitly.
Note that the actual file is not needed for this specific test case since the test is only extracting data from envs.
I have added three cases to cover, just make sure to fill with the expected data

func TestEnvStore_GetProviderPaths(t *testing.T) {
	tests := []struct {
		name      string
		envs 	  map[string]string
		wantPaths map[string][]string
	}{
		{
			name: "file provider",
			envs: map[string]string{
				"AWS_SECRET_ACCESS_KEY_ID": "file:FILEPATH",
			}
			wantPaths: map[string][]string{
				"file": {
					"FILEPATH"
				},
			},
		},
		{
			name: "vault provider",
			envs: map[string]string{
				// Add all the envs from https://github.com/bank-vaults/internal/blob/1d4670005e01baaa08bac7e17d0876d444d3286b/injector/injector_test.go#L92-L101
			}
			wantPaths: map[string][]string{
				"vault": {
					// fill expected
				},
			},
		},
		{
			name: "multi provider",
			envs: map[string]string{
				"AWS_SECRET_ACCESS_KEY_ID": "file:FILEPATH",
				"MYSQL_PASSWORD": "vault:secret/data/test/mysql#MYSQL_PASSWORD",
				"AWS_SECRET_ACCESS_KEY: "vault:secret/data/test/aws#AWS_SECRET_ACCESS_KEY",
			}
			wantPaths: map[string][]string{
				"vault": {
					// fill expected
				},
				"file": {
					// fill expected
				},
			},
		},
	}

	for _, tt := range tests {
		ttp := tt
		t.Run(ttp.name, func(t *testing.T) {
			// prepare envs
			for envKey, envVal := range ttp.envs {
				os.Setenv(envKey, envVal)
				t.Cleanup(func() {
					os.Unsetenv(envKey)
				})
			}

			paths := NewEnvStore().GetProviderPaths()

			for key, expectedSlice := range ttp.wantPaths {
				actualSlice, ok := paths[key]
				assert.True(t, ok, "Key not found in actual paths")
				assert.ElementsMatch(t, expectedSlice, actualSlice, "Slices for key %s do not match", key)
			}
		})
	}
}

[ramizpolic]

great work!