Fixes #34526 - Switch Rails version to 6.1

Changes overview:
- Set default Rails version to 6.1
- Required dynfow >= 1.6.5
- Cleanup deprecation warnings in config/as_deprecation_whitelist.yaml
- ActiveSupport::ParameterFilter instead of ActionDispatch::Http::ParameterFilter...

Fixes #34596 - sanitize default template names

Default boot templates are weirdly interconnected with its settings.

Fixes #32892 - add rails URL validator

We only exposed module implementing the URL validation, we should
provide a proper HTTP URL attributes validation.

This is much more convenient way to expose validations to new setting
DSL, so the only user of this validation `http_proxy` setting...

Refs #30840 - spelling findings after using eslint

Fixes #27788 - IPv6 support for trusted hosts

Fixes #27927 - allow taxonomy inheritance

Fixes #25702 - Deprecate Taxonomy-enabled related methods

This commit deprecates the following Taxonomy methods:
`Taxonomy.enabled?`, `Taxonomy.enabled_taxonomies`,
`Taxonomy.locations_enabled`, `Taxonomy.organizations_enabled`.
Since both taxonomies are now always enabled, these methods will always...

fixes #24935 - validate existence of proxy assocations

Fixes #19787 - Fix Layout/SpaceAfterComma cop

Fixes #21055 - use _id attributes for host taxonomy validator

Otherwise, the error messages are not visible.

Also log the host error messages as `error` instead of `info`, as it
should be more appropriate for this case.

Fixes #21829: Add association_exists_validator (#5405)

This validator ensures that an associated model (fk relation) actually
exists with the ID specified on this model. i.e. Hostgroup.realm_id

This PR is required for Katello to require a ContentFacet on a Host.

fixes #21694 - Add consistency validation for MTU and VLAN

Fixes #19907 - Configure Style/TernaryParentheses cop

Fixes #20890 - changes SSH key validation messages

Fixes #19677 - Add settings for local boot templates

Fixes #19947 - Fix creating bookmarks for global params

Fixes #19400 - defer loading of tables list cache

The BookmarkControllerValidator can get loaded sooner than the tables
are loaded (especially in tests).

fixes #18476 - users have ssh keys

Fixes #17228 - Select templates as global defaults (#4283)

This should allow user to select templates that will be used
for building PXE Default on TFTP proxy. These templates will
not be updated from seeds during updates.

Refs #15779 - make background processing unavailable for now (#4217)

The original PR got vetted in the packaging phase and including
foreman-task as dependency of Foreman was refused. We need to rethink
our approach for getting the foreman-tasks functionality available...

Fixes #15779 - make background processing available

Fixes #12543 - enable utf-8 encoding in email address

According to RFC 6532, the local part of an email address
can be non-ascii characters, and should support in utf-8.
The current email validation doesn't allow it,
so emails like Pelé@example.com and 我買@example.com are not supported

fixes #16725 - add plugin extension point for smart proxies

Fixes #16414 - reword alphanumeric validation error message

Fixes #15370 - Validate settings values

Adds validations for administrator, email_reply_address
and trusted_puppetmaster_hosts settings

fixes #14664 - support IPv6 in Nic, Hosts and Hostgroups models

Refs #3809 - Turning on some rubocop cops

fixes #14638 - Refactor Subnet into STI to allow different subnet types

Fixes #14198 - remote_addr validation accepts regex with digit matching

fixes #14225 - add missing require for Resolv

Setting itself is explicitly required too, which will provide a better
error message in future for this and similar issues loading the class.

Fixes #6924 - Additional validations for Setting

Fixes #6241 - Validations for associations with proxies

Fixes #12698 - Insufficient URL validation Smart Proxy and Medium.

Problem: The regex that validates smart proxies URLs only matches
'beginning of text'. This allows us to add just \n after a valid URL and
put anything after it. For instance, javascript:alert('hacked'). I...

Fixes #11953 - Add STI controllers to bookmark via permissions

Refs #3809 - Enable cop Style/IfUnlessModifier

Fixes #9439 - 'white spaces' changed to 'spaces' in validation error message

Fixes #9195 - register MAC validation errors properly

Fixes #8414 - extracts validators from models

Also cleans up some unused validators looking for trailing whitespace
that is stripped by the StripWhitespaces concern.
Tried to make some sense from unmatching regexps and validation error
messages. Some validations might need a different regexp to check for what...

fixes #5915 - Add support for Infiniband 64-bit MAC addresses