server: prepare DB schema for user attributes

First step of #67.

Cargo.lock

@@ -2453,6 +2453,7 @@ dependencies = [
  "serde_json",
  "serial_test",
  "sha2 0.10.6",
+ "strum",
  "thiserror",
  "time 0.3.19",
  "tokio",
@@ -2466,7 +2467,7 @@ dependencies = [
  "tracing-log",
  "tracing-subscriber",
  "urlencoding",
- "uuid 0.8.2",
+ "uuid 1.3.1",
  "webpki-roots",
 ]
 
@@ -2609,12 +2610,6 @@ dependencies = [
  "digest 0.10.6",
 ]
 
-[[package]]
-name = "md5"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "490cc448043f947bae3cbee9c203358d62dbee0db12107a74be5c30ccfd09771"
-
 [[package]]
 name = "memchr"
 version = "2.5.0"
@@ -4065,6 +4060,12 @@ version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
 
+[[package]]
+name = "strum"
+version = "0.24.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "063e6045c0e62079840579a7e47a355ae92f60eb74daaf156fb1e84ba164e63f"
+
 [[package]]
 name = "subtle"
 version = "2.4.1"
@@ -4530,10 +4531,6 @@ name = "uuid"
 version = "0.8.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bc5cf98d8186244414c848017f0e2676b3fcb46807f6668a97dfe67359a3c4b7"
-dependencies = [
- "getrandom 0.2.8",
- "md5",
-]
 
 [[package]]
 name = "uuid"
@@ -4542,6 +4539,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5b55a3fef2a1e3b3a00ce878640918820d3c51081576ac657d23af9fc7928fdb"
 dependencies = [
  "getrandom 0.2.8",
+ "md-5",
 ]
 
 [[package]]