76670: backup: move resolution from planning to exec r=dt a=dt

Release note (ops change): the cluster setting bulkio.backup.resolve_destination_in_job.enabled can be used to delay resolution of backup's destination until the job starts running.

76721: spanconfig: introduce new read-only system target r=arulajmani a=arulajmani

This patch is motivated by the host tenant's desire to fetch all system
span configurations it has installed over secondary tenants without
explicitly constructing targets for all tenant IDs in the system. This
is handy for the host tenant's reconciliation job, which populates an
in-memory view of all system span configurations to diff against the
state implied by the schema. This in-turn allows the host tenant to issue
targeted updates/deletes.

We introduce a new system target type to achieve this which allows a
tenant to request all system span configurations it has installed that
target tenants. This is only ever consequential in the context of the
host as only the host tenant can install system span configurations on
other tenants. We also make this target read-only, in that, we disallow
persisting its implied encoding in `system.span_configurations`. We add
validation to the KVAccessor to this effect.

While here, we also disallow creating span targets that overlap with
the reserved system span configuration keyspace.

Release note: None

----
Alternative approach to #76704

76757: ui: change invalid lease to expired lease on problem ranges page r=Santamaura a=Santamaura

When browsing the problem ranges page and invalid leases appears customers
regularly are concerned with this status as they interpret it as something
with the cluster is wrong which is often not the case. In order to imrpove this,
the invalid lease section has been changed to expired lease and there is a
description added below which explains that this status is often not a cause
for concern.

Release note (ui change): change invalid lease to expired lease on problem ranges page

Resolves: #38616

![Screen Shot 2022-02-17 at 3 06 19 PM](https://user-images.githubusercontent.com/17861665/154571094-4454f4e9-9cec-471c-8c41-48c6f1afd5a4.png)


Co-authored-by: David Taylor <tinystatemachine@gmail.com>
Co-authored-by: arulajmani <arulajmani@gmail.com>
Co-authored-by: Santamaura <santamaura@cockroachlabs.com>