Sources/inline: support lzma+base64 encoded data

Extend the inline source to support lzma compressed and base64 encoded
'data'. This will allow us to reduce the potential manifest size when
embedding big files. The aim is specifically at eventually embedding
SBOMs of the image.

An example single SBOM can be a JSON file with size of about 1.9 MiB.
The lzma+base64 combination reduces the 'data' to embed to "only" around
250 KiB.

Signed-off-by: Tomáš Hozza <thozza@redhat.com>

sources/org.osbuild.inline

@@ -13,6 +13,7 @@ resource is decoded and written to the store.
 
 import base64
 import contextlib
+import lzma
 import os
 import sys
 from typing import Dict
@@ -34,7 +35,7 @@ SCHEMA = """
         "properties": {
           "encoding": {
             "description": "The specific encoding of `data`",
-            "enum": ["base64"]
+            "enum": ["base64", "lzma+base64"]
           },
           "data": {
             "description": "The ascii encoded raw data",
@@ -70,7 +71,14 @@ class InlineSource(sources.SourceService):
         if os.path.isfile(target):
             return
 
-        data = base64.b64decode(desc["data"])
+        encoding = desc["encoding"]
+        if encoding == "base64":
+            data = base64.b64decode(desc["data"])
+        elif encoding == "lzma+base64":
+            data = base64.b64decode(desc["data"])
+            data = lzma.decompress(data)
+        else:
+            raise RuntimeError(f"Unknown encoding {encoding}")
 
         # Write the bits to disk and then verify the checksum
         # This ensures that 1) the data is ok and that 2) we