chip-tool: add more flexibility in PAA root folder selection

#### Problem

Fixes project-chip#21681 chip-tool: add more flexibility in PAA root folder selection

#### Change overview

If `--paa-trust-store-path` is not given, and the environment variable
`CHIPTOOL_PAA_TRUST_STORE_PATH` exists, use its value.

#### Testing

Manual confirmation of the logged `mPaaTrustStorePath.Value()`.

examples/chip-tool/commands/common/CHIPCommand.cpp

@@ -41,6 +41,7 @@ constexpr chip::FabricId kIdentityAlphaFabricId = 1;
 constexpr chip::FabricId kIdentityBetaFabricId  = 2;
 constexpr chip::FabricId kIdentityGammaFabricId = 3;
 constexpr chip::FabricId kIdentityOtherFabricId = 4;
+constexpr const char *kTrustStorePathVariable = "CHIPTOOL_PAA_TRUST_STORE_PATH";
 
 namespace {
 const chip::Credentials::AttestationTrustStore * GetTestFileAttestationTrustStore(const char * paaTrustStorePath)
@@ -99,6 +100,12 @@ CHIP_ERROR CHIPCommand::MaybeSetUpStack()
     factoryInitParams.listenPort = port;
     ReturnLogErrorOnFailure(DeviceControllerFactory::GetInstance().Init(factoryInitParams));
 
+    if (!mPaaTrustStorePath.HasValue()) {
+      char * const trust_store_path = getenv(kTrustStorePathVariable);
+      if (trust_store_path != nullptr) {
+        mPaaTrustStorePath.SetValue(trust_store_path);
+      }
+    }
     const chip::Credentials::AttestationTrustStore * trustStore = mPaaTrustStorePath.HasValue()
         ? GetTestFileAttestationTrustStore(mPaaTrustStorePath.Value())
         : chip::Credentials::GetTestAttestationTrustStore();
@@ -107,9 +114,9 @@ CHIP_ERROR CHIPCommand::MaybeSetUpStack()
     {
         ChipLogError(chipTool, "No PAAs found in path: %s", mPaaTrustStorePath.Value());
         ChipLogError(chipTool,
-                     "Please specify a valid path containing trusted PAA certificates using [--paa-trust-store-path paa/file/path] "
-                     "argument");
-
+                     "Please specify a valid path containing trusted PAA certificates using"
+                     "the argument [--paa-trust-store-path paa/file/path]"
+                     "or environment variable [%s=paa/file/path]", kTrustStorePathVariable);
         return CHIP_ERROR_INVALID_ARGUMENT;
     }