chore: add aliases to generate command options. (#3689)

Adding alias to repository-path and api-definitions-path to be
compatible with Librarian
[options](https://github.com/googleapis/librarian/blob/d3f78d51103c523da60251e790c05a681331192a/internal/command/flags.go#L40)

[click options](https://click.palletsprojects.com/en/stable/options/)
allows alias directly, so this change is trivial and does not affect any
existing usage cases.

Author: zhumin8

hermetic_build/library_generation/cli/entry_point.py

@@ -50,6 +50,7 @@ def main(ctx):
 )
 @click.option(
     "--repository-path",
+    "--output",
     type=str,
     default=".",
     show_default=True,
@@ -62,6 +63,7 @@ def main(ctx):
 )
 @click.option(
     "--api-definitions-path",
+    "--api-root",
     type=str,
     default=".",
     show_default=True,