Add persist/read-only Persistence Mode dropdown to Content Analytics app

Description

Epic #37349 ("Analytics: Environment Filtering") originally proposed making environment a first-class dimension of the Content Analytics pipeline, so an Authoring instance could select and read a Production instance's analytics data without creating users/roles for authorized personnel in Production.

The team has since concluded a simpler approach removes the need for cross-environment access entirely:

• Add a new input to the Content Analytics app config that lets the user decide whether this dotCMS instance persists analytics events to the Content Analytics infrastructure, or is read-only (queries/dashboards only, no ingest).
• Drop the idea of classifying or filtering analytics data by environment altogether. All events for a given tenant + project land in ClickHouse with no distinction of which environment emitted them, as long as the instance is configured by the Platform Team to access Content Analytics.
• This lets a customer flip persistence on/off per instance whenever needed (e.g. stop a UAT instance from writing events) without any environment-selector UI, environment identity plumbing, or cross-environment authorization work.

This supersedes the environment-required-at-ingest decision made in #37349's 2026-09-09 amendment (formalized under the dot-ca-event-manager constitution v1.2.0, Principle II, and specced under #37407): that work is being reverted as part of this pivot. The environment column already added to the ClickHouse tables stays in place for now (no schema migration) — it's simply no longer a required, enforced ingest parameter or a filtering dimension.

UI control decided (2026-09-14, Product Director): a dropdown, not a boolean toggle. The Content Analytics app config gets a "Persistence Mode" field with explicit values — "Read & Write" and "Read Only" — leaving room to add further modes later (e.g. "Disabled") without changing the field type again.

Acceptance Criteria

• The Content Analytics app config exposes a new "Persistence Mode" dropdown with values "Read & Write" and "Read Only"
• Instances that already have Content Analytics configured today default to "Read & Write" after upgrade — no customer silently stops sending events
• When Persistence Mode is "Read & Write", dotCMS core sends analytics events to the CAEM ingest endpoint exactly as it does today
• When Persistence Mode is "Read Only", dotCMS core does not call the CAEM ingest endpoint at all — enforced core-side, no CAEM-side rejection required
• Dashboard reads/queries work identically regardless of Persistence Mode — the setting only gates ingest, never reads
• Changing Persistence Mode takes effect without a dotCMS restart, consistent with other Content Analytics app config values
• Events from different environments of the same tenant + project are no longer distinguished anywhere in the pipeline — no environment selector, environment identity resolution, or cross-environment authorization is implemented
• The environment request parameter on POST /v1/event/ingest is no longer required/non-blank-validated — omitting or blanking it no longer produces a 400 (reverts the #37407 / constitution v1.2.0 Principle II behavior)
• Existing ingest integration tests that were updated to supply a required environment value are updated again to reflect it being optional, not deleted
• The environment column remains in the ClickHouse raw events and aggregate tables with no migration performed as part of this change

Additional Context

• Supersedes the environment-filtering approach in epic #37349 (not modified by this issue — team to close/amend separately)
• Reverts the required-environment-at-ingest decision from #37349's 2026-09-09 amendment, specced under #37407 (dot-ca-event-manager, specs/003-environment-filtering/spec.md)
• Gate: instance must already be configured/enabled for Content Analytics access by the Platform Team before this input is meaningful
• UI decision log: 2026-09-11 left toggle-vs-dropdown open for Product; 2026-09-14 Product Director chose the dropdown control type ("Read & Write" / "Read Only" as values); 2026-09-17 the field's label was refined from "Analytics Mode" to "Persistence Mode" during spec work — it names what's actually being decided (persist or not) instead of a vague "mode"