Reduce default values for ` --older-than` and `--keep` and explain output

[bittner]

The commands configmap, secret and image orphans have rather high default values for:

• --keep (default 10)
• --older-than (default "2mo")

While this might look like a somewhat "safe" choice than a smaller number,

1. we're talking about resources that we detect to be unused, and
2. it's irritating to run seiso without those options and not get any results.

We may need to consider typical developer patterns of use, such as:

"I've been developing heavily this week, and now I just hit the quota limit."

To me, this sounds like a common scanario. For a case like that "2 months" makes little sense: It makes seiso tell us, "No resources found", and yields the impression that the tool is broken.

Suggested solution

1. Reduce --keep default to 3
2. Reduce --older-than default to 1w
3. Explain the filters currently active in the result we print out, e.g.

   $ seiso configmaps -n myproject -l app=myapp
   Showing results for --keep=3 and --older-than=1w
   INFO Nothing found to be deleted.