[charts/druid, charts/portal] add PDB support

[jmmAVGO]

Description of the change

This PR allows the use of PodDisruptionBudgets (PDBs) for Portal containers. Though the default minAvailable setting is 1, pdb: create is set to 'false' by default. Thus, PDBs are disabled unless otherwise specified.

Benefits

These changes facilitate more resilient Portal deployments.

Drawbacks

Users should be familiar with PDBs before utilizing them.

Additional information

Please note that this PR makes me realize that GW/OTK charts don't specify a minAvailable or maxUnavailable value (they must be specified by the user). This PR is slightly different. We should probably adopt a uniform approach; either I should modify this PR to match those, or I should create subsequent PRs to make those match this one. Thoughts?

Checklist

• [x] Chart version bumped in Chart.yaml according to semver.
• [x] Variables are documented in the README.md
• [x] Title of the PR starts with chart name (e.g. [charts/gateway])
• [x] If the chart contains a values-production.yaml apart from values.yaml, ensure that you implement the changes in both files

[jmmAVGO]

Do you all have thoughts on setting default minAvailability (typically to one) to 1 vs. not setting a value? Like I said, this takes a different approach than gw/otk, and I think we should be consistent with whichever we choose.