Add the ability to see diff between revisions

[nabokihms]

Problem

The main idea is that it is sometimes required to see what changes between module runs. For example, resources were redeployed because a value was changed, and you want to know why exactly this happened.

Proposal

Add the command to see module revisions.

module revision # lists all revisions
module revision 513 --manifests # shows manifests of the particular revision
module revision 513 --values # shows values of the particular revision

With this, the following scenarios are possible:

1. Compare the current render with the previous revision:

diff -u <(module render) <(module revision 513 --manifests)

2. Compare two previous revisions:

diff -u <(module revision 513 --manifests) <(module revision 512 --manifests)

3. Compare current values with the values from the previous revision:

diff -u <(module values) <(module revision 513 --values)

4. Compare values from two previous revisions:

diff -u <(module revision 513 --values) <(module revision 512 --values)