Add swtpm-based integration tests for the TPM functionality. The test
suite checks whether swtpm v0.10.1 is available and if it's being run as
root and if so runs a set of tests against swtpm instances of different
configurations (1.2, 2.0, uninitialized, etc...) to validate the client
behavior.
Updates tailscale/corp#34174
Signed-off-by: Patrick O'Doherty <patrick@tailscale.com>