docs: Update old or missing license headers

[orpheuslummis]

Some license headers were missing or not updated in the v0.2.0 release and with the inclusion of the p2p PRs, so correcting the situation here.

[jsimnz]

Everything in the net/ package we are explicitly licensing under Apache 2, and foregoing any copyright. See the comment here in net/doc.go

defradb/net/doc.go

Lines 33 to 37 in 27db5f5

	Credit: Some of the base structure of this net package and its
	types is inspired/inherited from Textile Threads
	(github.com/textileio/go-threads). As such, we are omitting
	copyright on this "net" package and will release this folder
	under the Apache 2.0 license as per the header of each file.

[jsimnz]

Does mean we need to add an Apache 2.0 license header to these files under net/

[orpheuslummis]

@jsimnz please double check the APL license header

Copyright © 2022 Democratized Data Foundation

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

[jsimnz]

I think just

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

is fine for the net/ package

[orpheuslummis]

Now the code files (not the autogenerated ones) under /net have license header APL. I included all files under /net instead of just the files of the top-level net package. If that's okay, it should be ready.

[jsimnz]

LGTM