PG raster, bugfixes and SQL filter

[elpaso]

A set of bugfixes, tests and a new little feature in PG raster provider:

• fixes Cannot instantiate the 'postgresraster' data provider when load raster from postGIS #34823
• unlock set filter sql in data source manager for PG raster
• add tests for multiple rasters in a single table (not tiled!)
• add other corner test cases (text pks, composite pks, no extent etc.)
• try to re-enable tests on Travis

Funded by ARPA Piemonte

[elpaso]

unrelated test failures on windows

[qgis-bot]

The backport to release-3_12 failed:

The process 'git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release-3_12 release-3_12
# Navigate to the new working tree
cd .worktrees/backport-release-3_12
# Create a new branch
git switch --create backport-34846-to-release-3_12
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick d6821a94cff8c917315f5494fff6daab8e01f5f5
# Push it to GitHub
git push --set-upstream origin backport-34846-to-release-3_12
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release-3_12

Then, create a pull request where the base branch is release-3_12 and the compare/head branch is backport-34846-to-release-3_12.